Rebellion is stirring in the laid-back Pacific island nation of Samoa, with threats to torch buses and stage mass demonstrations all over the official plan to oblige citizens to drive on the left.

Thanks to a brief period of German rule in the early 20th century, Samoans have always driven on the right. The Government plans to change that on September 7, making it the first country to swap sides since Ghana in 1974.

The rationale is that the switch will encourage Samoans' relatives in Australia and New Zealand to send home their used right-hand-drive cars. At present, most vehicles on the streets of the archipelago are gas-guzzling American left-hand drives.

But locals are not happy, fearing that accident rates will soar and that their left-hand-drive cars will become worthless.

A campaign of civil disobedience has begun, with signs reminding drivers to "keep left" after September 7 removed and newly painted arrows on roads altered to point in the opposite direction. Two villages have threatened to force motorists to keep right when passing through.

Twenty-four bus operators are refusing to remodel their vehicles so that passenger doors are on the left, as it is too costly.

They dismissed a government offer of $650 compensation per bus as derisory. Nanai Tawan, of Mapuitiga Transport said: "The Government thinks we are fools. In protest I would rather bring my buses to parliament and burn them there for parliament to see what they are doing to us."

The changeover was the idea of Prime Minister Tuilaepa Sailele Malielegaoi, who has been criticised for failing to consult Samoans or order a feasibility study. He has also angered many by claiming it takes only three minutes to learn how to drive on the left.

Opponents have not been pacified by the establishment of a test track where drivers can practice, nor by the announcement of public holidays on September 7 and 8 to help locals adjust to the new arrangement.

A demonstration planned for Monday in the capital, Apia, is expected to draw thousands of protesters, and an action group, People Against Switching Sides (PASS), is pursuing legal action in the Supreme Court, claiming the move is unconstitutional.

The plan has aroused passions rarely seen in Samoa and has already triggered the nation's two largest street protests. Veo Papa of PASS said such reactions were not surprising.

"They [Samoans] have to be able to express their frustration in some way," she said. "I just hope that the frustration and anger as we approach the day ... is not going to spark violence."

PASS is hoping the switch will be halted by the court. An Australian engineering expert, Thomas Triggs of Monash University, has testified that accidents and road deaths are likely if it goes ahead.

"Habit is extraordinarily difficult to change," he said, adding that pedestrians were most at risk.

A New Zealand expert, Graham Williams, predicted a "dramatic increase" in the number of crashes and expressed concern about rural areas, where no one wore seatbelts on the narrow roads which were riddled with potholes and speedhumps.

While Samoa's neighbours in American Samoa drive on the right, most of the Pacific including a clutch of former British colonies uses the left.