Operators of Bangkok's green mini-buses must cease services from today or face arrest, the Transport Ministry says.

Transport officials will patrol city streets and arrest operators who continue to run the vehicles after today, Deputy Transport Minister Suchart Chokechaiwatanakorn, who oversees bus services, said yesterday.

"The Transport Ministry will not extend the deadline again," he said.

"This is to improve the public transit service for the sake of passenger safety and quality of life."

Mini-bus operators may rally at the Royal Plaza today to demand the deadline be extended.

The ministry had given operators five years to replace their old buses with new vehicles.

Operators who flout the deadline will be arrested and lose their licences, he said.

The deadline could be extended on a case-by-case basis for individual operators who might have been cheated by their bus suppliers, he said.

The operators must file for an extension with the ministry which will decide on the matter within 15 days.

Today's deadline affects about 700 green mini-buses.

The state Bangkok Mass Transit Authority (BMTA) has prepared about 500 substitute buses which Mr Suchart said would be enough to maintain existing services.

He said operators of the green mini-buses were required to commission new orange or yellow, natural gas-fuelled buses.

BMTA staff yesterday expressed support for the ministry's policy. But some 50 green mini-bus operators submitted a letter asking Prime Minister Abhisit Vejjajiva to extend the deadline for another six months.

Sunimit Meethip, head of a mini-bus operators' club, said the group operated about 400 green mini-buses but had only been able to procure 38 new buses because the Land Transport Department had not endorsed the import of other buses from China.

The operators would lose 1,600 baht in income a bus a day if the Transport Ministry imposed the ban from today, he said.

Mr Sunimit said the operators had been slow to buy replacement buses, but that was because they could not secure funding.