KIEV (AFP) - Flames engulfed Kiev's occupied Independence Square on Wednesday as police stormed the main protest camp in a bloody escalation of Ukraine's three-month political crisis which left at least 16 people dead.

A defiant President Viktor Yanukovych refused a chorus of calls from global leaders to halt the ferocious assault on the bloodiest day since protests broke out in November, when he ditched a pact with the EU in favour of closer ties with former Soviet master Russia.

The scene was apocalyptic as explosions echoed around central Kiev and the iconic square turned into a war zone.

Helmeted protesters hurling rocks, fireworks and Molotov cocktails fought back against black-armoured riot squads targeting them with stun grenades and water cannon.

Smoke from burning tyres billowed up into the icy night air, while laser lights, flags and the glare of several fires from burning tents flickered over the riled-up crowd.

"Yanukovych said that there is only one option... to clear Maidan and that everyone has to go home," opposition leader Vitali Klitschko said after a meeting with the president, using the local name for the square.

Several protesters ran or were stretchered out of their last stronghold, the imposing Trade Union House building on the square, as it went up in flames.

"If we hold on until morning, we have a chance to make it out," one protester said.

Kiev was essentially in lockdown as authorities halted the city's metro system and limited road traffic coming into the capital.

Police said seven officers died from gunshot wounds, while authorities and medics counted nine civilian deaths since Tuesday morning.

Another two civilians were found dead, but their bodies showed no exterior signs of violence, making it unclear how they had died.

More than 150 people were injured, including dozens of police officers, some with serious wounds.