Throngs of anti-government protesters remained in control of parts of central Kiev on Monday morning, as police kept their distance and Viktor Yanukovych's government pondered its next move.

After huge protests on Sunday, during which several hundred thousand people took to the streets of Kiev to call for the president's removal, protesters erected makeshift barricades around Independence Square – the hub of the 2004 Orange Revolution. Nearby, the main City Hall building was taken over by protesters without police resistance on Sunday evening.

Many of the windows were smashed and "Revolution HQ" was daubed in black paint on its stone Stalinist facade. Inside, hundreds of people milled around receiving refreshments; many who had travelled from the regions to Kiev were sleeping on the floor.

"We've just had enough. We're sick of this," said Alexander Yabchenko, a 33-year-old oncologist from Lviv in western Ukraine, who had travelled to Kiev to take part in the protests and was now offering medical help to those injured in the clashes at a makeshift medical centre inside the town hall. "I'm not part of any political party but I understand that only by trying to be more European can we end our troubles. Even from my own experience, I see so many problems with the medical system, and we just need to modernise."

The protests began after Yanukovych walked away from an integration pact with the European Union that was supposed to be signed at a summit in Vilnius last Friday in favour of closer relations with Russia. The mood intensified when police cleared Independence Square with considerable force early on Saturday and banned further protest. The residents of Kiev ignored them, pouring into the square in vast numbers on Sunday, in a largely peaceful protest that turned violent at the fringes.

On Monday morning, as Kiev began its working week, tension was high as both ordinary people and opposition leaders were left guessing how events might unfold. Hundreds of protesters took up positions blocking entrances to government buildings to stop officials from getting to work, while others blocked off whole streets. Many of the people who spent the night in the two government buildings seized by protesters insisted they would not leave until the government fell.

In the western city of Lviv, a stronghold of pro-European forces, the regional authorities announced a general strike on Monday.

The key political opposition to Yanukovych, such as the jailed former prime minister Yulia Tymoshenko and the heavyweight boxer Vitali Klitschko, have called on their supporters to refrain from violence but not to go home.

Protesters are seen near barricades which blocked a street in Kiev. Photograph: Vasily Fedosenko/Reuters

"This government is clearly over," said Vladimir Luchishin, 60, from Donetsk, who was sleeping at city hall, having arrived on Sunday. "If they try to fight back with force, it will only make things worse for them."

Police have retreated from most of the centre of Kiev but cordons of riot police remained in position, guarding the presidential administration – the scene of violent clashes on Sunday in which more than 100 police were injured. On Monday morning, the interior ministry said a total of 150 riot police and other officials had been injured, while 165 protesters had been injured, 109 of which required some kind of hospital treatment.

Yanukovych is due to travel to China on Tuesday, calling into Moscow on the way back to discuss economic help from Russia, but in the current climate it is unclear whether he can make the trip. Except for brief remarks posted on his website on Saturday, condemning violence against protesters and promising that Ukraine would not give up on EU integration, he has not commented publicly on the situation.