A convoy of cars carrying protesters drove across Malaysia on Monday in the latest demonstration against an Australian rare earths plant that activists claim will produce dangerous radioactive waste.

It came as demonstrators launched a hunger strike in the capital Kuala Lumpur in protest at the plant run by Lynas Corp, which began processing rare earths last month after a delay of more than a year due to strong opposition.

The Australian miner hopes the $800-million plant can help break the Chinese stranglehold on the market for rare earths, used in everything from missiles to mobile phones, but the project has been dogged by controversy from the start.

Some 100 activists in 20 cars wearing green T-shirts began their protest from the headquarters of the opposition Pan-Malaysian Islamic Party, located just outside the capital Kuala Lumpur.

At least 150 cars are expected to join the convoy during the six-hour journey to the Lynas plant in eastern Pahang state, organisers said.

"It is our struggle to bring down this corrupt regime and evict Lynas from Malaysia," said activist Wong Tack, chairman of the "Himpunan Hijau" movement which is spearheading the anti-Lynas campaign.

He was referring to the ruling Barisan Nasional coalition which has backed the Lynas facility in the industrial area of Gebeng. Anti-Lynas campaigners have vowed to support the opposition in elections due by the end of June.

The protest will culminate with a rally and a candlelit vigil outside the Lynas plant, said Wong.

In central Kuala Lumpur, more than 30 people including children began a 100-hour hunger strike to oppose the Lynas refinery.

"We must protect our environment," said one participant, Tan Wen Shi, a 15-year-old student.

Residents and activists say the plant will release radioactive gases and solid waste such as radium and lead, as well as small amounts of uranium.

But Lynas has insisted that any radioactive waste would be low-level and not harmful and that it would be safely disposed of.