Around a thousand protesters blocked off the Ukrainian government’s main headquarters in Kyiv on Monday.
The opposition has called for more protests and a national strike to force the resignation of President Yanukovych after he refused to sign a trade pact with the EU.
Hundreds of activists spent the night in Independence Square and say they are preparing for round-the-clock demonstrations.
Others barricaded themselves inside the City Hall where they have set up their headquarters. Staff were still being allowed to come in and do their usual jobs.
On Sunday hundreds of thousands took part in a march, defying a ban on rallies.
Many have joined the protests in anger at the violent treatment of protesters by riot police.