Helicopters flew overhead and riot police fired teargas as they moved into Bahrain's Pearl roundabout early on Wednesday, March 16, to clear protesters camped out there for weeks, a witness said.

According to Reuters, protesters threw petrol bombs at police who advanced in thick lines from the Bahrain Financial Harbour, the main financial district of the capital Manama, firing dozens of rounds of teargas.

Helicopters buzzed overhead as youths ran toward police in waves and scattered when new rounds of teargas hit.

The security operation came a day after Bahrain's king declared martial law as his government struggled to quell an uprising by the island's Shi'ite Muslim majority that has drawn in troops from fellow Sunni-ruled neighbor Saudi Arabia.

It was not clear if Gulf Arab forces invited in by the government for support were involved in the operation.