Six police vehicles were damaged, at least one set on fire, and national police chief Adul Saengsingkaew admitted the situation remained very tense.
Pol Gen Adul called an urgent meeting with the Police Region 8 officers shortly after the latest clash at Khuan Nong Hong intersection in Cha-uat district of the southern province. The situation at the protest site was very worrying, he said.
The angry farmers reportedly used the damaged vehicles to again block Highway 41, the main road connecting the central and southern regions.
PM's Office Minister Varathep Rattanakorn called on the farmers to end their protest in support of demands for a guaranteed price for their sheet rubber, initially 120 baht, and instead accept the government's offered subsidy.
Other officials have also called for an end to the blockades which affect road traffic, business and tourism in the South.
Prime Minister Yingluck Shinawatra on Sunday asked the farmers to cease their demonstrations and clear the roads for traffic.
The government has approved a 2,520 baht subsidy per rai for rubber farmers, limited to 25 rai per farmer, to help them overcome problems caused by sagging prices and high production costs. This is equivalent to 90 baht per kilogramme for unsmoked rubber sheet, according to the government. Most farmers accepted the offer, but the protesting group continued to demanded 100 baht.
Supported by some palm oil growers, they set up blockades on Saturday at Khuan Nong Hong and Ban Tao Poon intersection in Chulabhorn district.
The blockades continued at the two spots on Sunday. The protesters later ended the blockade at Ban Tao Poon but continued to block Highway 41 at Khuan Nong Hong.
About 7am on Monday, about 200 police led by Pol Col Suthas Charnsawat, the deputy police chief of Nakhon Si Thammarat, cleared the protesters from Khuan Nong Hong and re-opened the highway for traffic.
Around noon, about 200 rubber and oil palm growers, most of them young men, returned to the intersection. Forty minutes later, they surrounded the police and threw bricks and other objects at them. The police retaliated, included firing tear gas to disperse them. During the clash both sides reportedly suffered injuries.
One protester was seriously injured and six police vehicles were reported to have been set on fire or seriously damaged, police said.
The police reportedly withdrew about one kilometre from the intersection after the clash, leaving the protesters again in control of the main road junction.