About 52 were killed and more than 206 others injured so far during fierce clashes between gunmen and police in Iraq's Shiite holy city of Karbala, which initially erupted on Monday night, a local police source said on Tuesday evening.

The Iraqi authorities had imposed curfew in Karbala, ordering dozens of thousands of Shiite pilgrims to evacuate the city, the source from Karbala police told Xinhua on condition of anonymity.

"The security forces in Karbala ordered curfew on Tuesday until further notice after sporadic clashes continued in the holy city," the source said.

The security forces also started to evacuate the pilgrims from the city center where clash re-erupted in the afternoon between gunmen and the Iraqi security forces, the source said.

Many police vehicles, ambulances and civilian cars were destroyed by the clashes, while the town was in chaos with hundreds of pilgrims running in all directions to avoid the heavy shootout and explosions of rocket-propelled grenades near the holy shrine, he said.

On Monday night, the holy city of Karbala, some 110 km south of Baghdad, became the scene of turmoil when clashes broke out between pilgrims and security forces near the holy shrine of Imam Hussein and the adjacent shrine of his brother Imam Abbas, the police said.

The clashes broke out after pilgrims and gunmen attacked a security checkpoint near the shrines, killing four people and wounding some 20 others, they said.

Earlier on Tuesday, the pilgrims gathered in the city peacefully after Shiite clerics called for calmness on Monday night.

Thousands of Shiite pilgrims are converging in Karbala to celebrate the 9th century birth of Muhammad al-Mahdi, the last of 12 Imam Shiites most revered.

Shiites believe that Imam Mahdi is hidden and will never die, but he will return at the end of the time to bring peace and justice to the mankind.

(Xinhua News Agency August 29, 2007)