Missiles pounded the Ukrainian capital of Kyiv on Friday as Russian forces pressed their advance and Ukrainian President Volodymyr Zelensky pleaded with the international community to do more, saying the sanctions announced so far were not enough.

Air raid sirens wailed over the city of three million people, where some were sheltering in underground metro stations, a day after Russian President Vladimir Putin launched an invasion that has shocked the world. A Ukrainian official said a Russian plane had been shot down and crashed into a building.

Ukrainian military vehicles are entering Kyiv to defend it against approaching Russian troops, Ukraine's interior ministry said on Friday, as the Russian invasion entered Day 2 and people in the capital scrambled to try and find safety.

Kyiv Mayor Vitali Klitschko said earlier the city had "entered into a defensive phase."

An estimated 100,000 people fled as explosions and gunfire rocked major cities in Ukraine. Dozens have been reported killed. Russian troops seized Chornobyl, the former nuclear power plant north of Kyiv, as they advanced on the city from Belarus.

In a hotel in the city centre, guests were directed to a makeshift basement shelter, lined with piles of mattresses and bottles of water. Workers — all local university students — served tea and cookies. Some people ducked out to a courtyard to smoke or get fresh air.

"We're all scared and worried. We don't know what to do then, what's going to happen in a few days," said one of the workers, Lucy Vashaka, 20.

Ukraine's Deputy Defence Minister Hanna Malyar added that Ukrainian army units were defending positions on four fronts, despite being outnumbered.

Russia makes claim it controls airport

However, reports emerged later Friday that the Russian military claimed it has taken control of an airport just outside Kyiv, as Kremlin forces bore down on the Ukrainian capital. The claim could not be independently verified.

Taking possession of the airport in Hostomel, which has a long runway allowing the landing of heavy-lift transport planes, would mean Russia can airlift troops directly to Kyiv's outskirts. Hostomel is just seven kilometres northwest of the city.

Russian Defence Ministry spokesperson Maj.-Gen. Igor Konashenkov said Friday that the Russian air forces used 200 helicopters to land in Hostomel and killed more than 200 troops belonging to Ukraine's special forces. Konashenkov claimed that Russian troops suffered no casualties.

That contradicts Ukrainian claims that Russian troops sustained heavy casualties in the fighting there.

The interactive features of this map will be active in future updates.

U.S. and Ukrainian officials say Russia aims to capture Kyiv and topple the government, which Putin regards as a puppet of the United States.

Zelensky, who in a statement posted online talked about the terrible explosions over Kyiv, said he understood Russian troops were coming for him but vowed to stay in the city.

"[The] enemy has marked me down as the No. 1 target," Zelensky said in a video message. "My family is the No. 2 target. They want to destroy Ukraine politically by destroying the head of state.

"I will stay in the capital. My family is also in Ukraine."

In his remarks, the Ukrainian leader warned that military and civilians were under Russian attack. He urged citizens to help one another and "stop the enemy wherever you see it."

Ukraine, he said, is defending its country alone with powerful forces watching from a distance.

"Did yesterday's sanctions convince Russia? We hear in our sky and see on our earth that this is not enough," the president said. "Foreign troops are still trying to become more active in our territory."

The UN human rights office said it was receiving increasing reports of civilian casualties, with at least 25 deaths verified, mostly from shelling and airstrikes.

"The figures, we fear, could be much higher," agency spokesperson Ravina Shamdasani said.

Asked if he was worried about Zelensky's safety, U.S. Secretary of State Antony Blinken told CBS: "To the best of my knowledge, President Zelensky remains in Ukraine at his post, and of course we're concerned for the safety of all of our friends in Ukraine — government officials and others."

Russia launched its invasion by land, air and sea on Thursday following a declaration of war by Putin, in the biggest attack on a European state since the Second World War.

The Kremlin said Russia is ready to send a delegation to Belarus in response to Zelensky's offer to discuss a non-aligned status for his country.

A democratic nation of 44 million people, Ukraine voted for independence at the fall of the Soviet Union and has recently stepped up efforts to join the NATO military alliance and the European Union, aspirations that infuriate Moscow.

Putin has said Russia is carrying out "a special military operation" to stop the Ukrainian government from committing "genocide" — an accusation the West calls a baseless fabrication. He said Ukraine is an illegitimate state whose lands historically belong to Russia, a view which Ukrainians see as an attempt to erase their more than 1,000 year history.

Putin's full aims remain obscure. He has said he does not plan a military occupation, only to disarm Ukraine and remove its leaders. But having told Ukrainians their state is illegitimate, it is hard to see how he could simply impose a new leader and withdraw. Russia has floated no name of a figure it would regard as acceptable and none has come forward.

Britain said Moscow's aim was to conquer all of Ukraine, and its military had failed to meet its main objectives on the first day because it failed to anticipate Ukrainians would resist.

Russia faces sweeping sanctions, trade limits

Western countries unveiled financial sanctions on Moscow billed as far stronger than earlier measures, including blacklisting its banks and banning technology imports. However, they stopped short of forcing Russia out of the SWIFT system for international bank payments, drawing strong words from Kyiv, which says the most serious steps should be taken now.

The European Commission on Friday warned Moscow that the European Union could impose more sanctions on Russia over its invasion of Ukraine, a day after EU leaders agreed on a robust package of measures.

"When it comes to the sequencing of packages, we have always said we have a massive package prepared and we will be applying this package in a progressive way, responding to concrete actions by Russia, and we are not at the end," spokesperson Peter Stano told a news conference.

The UN Security Council was set to vote on Friday on a draft resolution that would condemn the invasion and require Russia's immediate withdrawal, though Russia is certain to veto it. China, which signed a friendship treaty with Russia three weeks ago, has refused to describe Moscow's actions as an invasion.

Russia has also prepared a package of retaliatory sanctions, the TASS news agency reported.

What's happening on the ground?

The situation on the ground is changing rapidly as Russian forces advance from several directions. But here's a glimpse at what's happening in some major centres as the fight in Ukraine moves into its second day.

Kyiv

Among the signs that the Ukrainian capital was increasingly threatened, the military said Friday that a group of Russian spies and saboteurs was seen in a district on the outskirts of Kyiv, and police told people not to exit a subway station in the city centre because there was gunfire in the area.

Ukrainian forces downed an enemy aircraft over Kyiv early on Friday, which then crashed into a residential building and set it ablaze, said Anton Herashchenko, an adviser to the interior minister. It was unclear whether the aircraft was manned or whether it could be a missile. Kyiv municipal authorities said at least eight people were injured when the object crashed into an apartment block.

The violence forced many to seek safety underground, with people moving into metro networks and basements in search of safety from air assaults.

Western border communities

In the west of Ukraine, people are moving to border crossings as they try to enter neighbouring countries, including Hungary, Slovakia and Poland.

Eastern communities

As Russian troops continued pressing their offensive Friday, intense fighting also raged in the country's east. Russian troops entered the city of Sumy, near the border with Russia, that sits on a highway leading to Kyiv from the east. The regional governor, Dmytro Zhivitsky, said Ukrainian forces fought Russian troops in the city overnight, but other Russian convoys kept rolling west toward the Ukrainian capital.

"Military vehicles from Sumy are moving toward Kyiv," Zhivitsky said. "Much equipment has passed through and is heading directly to the west."

Zhivitsky added that another northeastern city, Konotop, also came under siege. He urged residents of the region to fight the Russian forces.

Donetsk and Luhansk

Humanitarian issues are a pressing concern as fighting intensifies in Ukraine, including in the country's restive east, where Ukrainian forces have been locked in conflict with Russian-backed separatists for nearly eight years. UN humanitarian chief Martin Griffiths said $20 million US from the UN's Central Emergency Response Fund will support emergency operations along the contact line in eastern Donetsk and Luhansk, and in other areas of the country, and will "help with health care, shelter, food, and water and sanitation to the most vulnerable people affected by the conflict."