Kyiv residents are under a 35-hour curfew from Tuesday evening until Thursday morning after Russian air strikes and shelling killed dozens of people in the city.
Vitali Klitschko, the capital of Ukraine’s mayor, announced that civilians will have to stay home from Tuesday 8pm local time (6pm GMT).
The curfew will last until 7am local time (5am GMT) on Thursday.
Russia’s invading troops have tightened their grip on Kyiv and escalated their attacks in their attempts to seize it.
“Today is a difficult and dangerous moment,” Mr Klitschko said as he announced the curfew.
“The capital is the heart of Ukraine, and it will be defended. Kyiv, which is currently the symbol and forward operating base of Europe’s freedom and security, will not be given up by us.”
A 15-storey residential tower block in west Kyiv caught fire after it was hit by an artillery strike.
Images showed a body in a bag on the ground, and firefighters tackled the blaze, helping evacuate residents trapped in the building.
Dozens of people were killed when four multi-storey buildings were also bombarded, Ukrainian president Volodymyr Zelensky said.
One blast sent shockwaves that tore through the entrance of a subway station in central Kyiv that was being used as a bomb shelter.
The Artem weapons factory in central Kyiv was also hit, with footage taken by a local resident showing smoke rising from the roof.
On Monday, Russia had urged workers of weapons factories – and residents in those areas – to stay away and warned it planned to attack the compounds to retaliate against a strike on the separatist-controlled city of Donetsk, that Ukraine has denied launching.
Mr Klitschko called for more men – who took their partners and children to western Ukraine so that they could flee the country – to return to the capital to defend it.
As Russia stepped up its assault on Kyiv, the leaders of Poland, the Czech Republic and Slovenia travelled to the city to show support for Ukraine.
On Monday, Fox News cameraman Pierre Zakrzewski was killed in Kyiv after the vehicle in which he was traveling was struck by incoming fire.
His colleague Benjamin Hall has remained in hospital, Fox News CEO Suzanne Scott said in a message to staff.
Mr Zakrzewski was the second journalist killed while covering the Ukraine conflict.
Brent Renaud, an American filmmaker and journalist, was shot dead by Russian forces in the town of Irpin, a regional police chief said on Sunday.
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