Rubber farmers have clashed with security forces in southern Thailand as protesters torched cars and police fired tear gas, officials said.
More than two dozen police officers were injured and 11 protest leaders were arrested as the demonstration in Prachuap Khiri Khan province over falling rubber prices turned violent late on Thursday, according to the authorities.
Two vehicles, apparently belonging to local media, were set ablaze during the clashes, which flared after some 400 farmers tried to block a major highway to the south of the country, provincial police commander Major General Thanet Soonthornsuk told AFP news agency.
"Twenty-five police officers were wounded. Two of them are in a serious condition after they were hit on the head by rocks," he said, adding that demonstrators had thrown acid at him.
Thailand is the world's top exporter of natural rubber and mounting anger among the kingdom's rubber farmers over their falling incomes poses a fresh challenge to Prime Minister Yingluck Shinawatra's two-year-old government.
In recent days angry rubber farmers have blocked roads, train lines and even, briefly, the entrance to an airport in Thailand's south where plunging global prices for the commodity have hit the local economy hard.
The region is a heartland of the opposition Democrat Party.
Yingluck's government has so far rejected demands to guarantee a rubber price of $3.7 per kilo which farmers later reduced to about 50 percent higher than the current price on world markets.
Deputy Prime Minister Pracha Promnog said he would travel to the south later Friday to meet protest leaders.
"We will open talks with them at all levels," he told reporters, without revealing if the government was ready to make concessions.