Protest organizer Sergei Milnichenko said tear gas had also been used as police moved in at about 04:30 on Saturday.
It followed fresh rallies against President Viktor Yanukovych’s refusal to sign an EU association agreement.
Unconfirmed reports said a number of people had been hurt.
Police said they had decided to clear Independence Square after “a number of incidents”, Interfax Ukraine news agency reported.
It was not clear what incidents they were referring to.
More than 1,000 people, most of them students, were in the square when police moved in, activists said.
Witnesses said ambulances were on the scene and some demonstrators were seen bleeding from their heads and arms.
Opposition MP Andriy Shevchenko tweeted that dozens of people had been hurt and at least 33 taken into police custody.
Reuters news agency said the injured included one of its cameramen and a photographer, who was left bloodied by blows to the head.
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