Protesters demanding farmer subsidies to offset losses from falling world rubber prices clashed with police in Thailand Thursday evening, throwing bricks and acid-filled bottles at the officers, authorities said.

Twenty police officers and four rescue volunteers were injured in the clash as protesters blocked a main road in Bang Saphan district in Prachuap Khirikhan province, Deputy Prime Minister Pracha Promnok said Friday.

He said one of the officers had a concussion and was in intensive care.

Video footage from TV channel ThaiPBS showed burning cars and masked protesters throwing glass bottles and shooting slingshots at police early Friday morning on a main road in Bang Saphan, over 360 km south of Bangkok.

In a telephone interview Songklod Cheunchoopol, an anti-government ex-soldier who joined the protest Thursday, accused the police of shooting giant firecrackers that caused the villagers to panic and trigger the police response. He said the police used tear gas but did not fire any gunshots.