A motorcyclist set on fire a car owned by an activist campaigning for the Election Commission's impeachment in the early hours of Monday.

Ekachai Hongkangwan told Lat Phrao police on Monday his car was gutted by the blaze. 

He had returned home after attending a rally against the poll agency on Sunday and parked his car outside his house in Bang Kapi district.

He said security camera footage showed two motorcycles entering the soi about 1am on Monday. One of the riders, still wearing a helmet went up to his car, poured a liquid over it and then set it alight. The two motorcyclists then left the soi, he said. 

Mr Ekachai said he had left the petition document used to collect signatures inside the car. It was partly burned.

Mr Ekachai was with a group that set up a desk outside a McDonald's outlet near Ratchaprasong intersection on Sunday to gather signatures supporting the impeachment of the election commissioners for alleged mismanagement of the polls on March 24.

He posted photos of the burned-out car and damaged petition paper on his Facebook account. The car was towed to the police station, where investigators would examine it for evidence.

Police said investigators would examine  recordings from other security cameras in the area, track the escape route of the arsonists and try to locate them. The case would be handled without prejudice, they added. 

It was the second attack on Mr Ekachai's car. The same car was set on fire and the left side slightly damaged about 3am on Tuesday last week. He registered a complaint about that attack at the same police station. 

Mr Ekachai was convinced the two incidents were political.