Police issued a stern warning on Tuesday against dek waen motorbike riders who have returned to take over the roads of Bangkok and some provinces after the government lifted the night-time curfew on Sunday.
The warning was issued on Tuesday by Pol Lt Gen Damrongsak Kittiprapas, the assistant national police chief.
Prime Minister Prayut Chan-o-cha on Monday issued a warning saying the government would reimpose the night-time curfew if people failed to cooperate with Covid-19 control measures.
Gen Prayut's warning followed media reports saying young motorcyclists, or dek waen, gathered for illegal street races on Sunday night shortly after the curfew was lifted.
According to the authorities, people have filed complaints about motorbike racing on major roads in Bangkok and some provinces.
"Police will take tough legal action against these dek waen," Damrongsak said.
He said six of them had been arrested in Songkhla.
The racers, aged 15-18 years old, were arrested for disturbing the peace after they gathered for illegal street racing on Sunday night after the night-time curfew was lifted, he said, adding their motorbikes were confiscated.
Damrongsak said each racer was fined 1,000 baht while three of them were told to pay additional fines of 500 baht each for driving without a licence.
The parents were fined for allowing the teenagers to go out at night, he said.
Members of the public are encouraged to report illegal street racing.
