A controversial Malaysian state boss who has faced mounting accusations of corruption and environmentally disastrous policies announced his resignation on Wednesday but is expected to retain influence from behind the scenes.

One of Malaysia's most powerful political figures, Taib Mahmud, 77, has been chief minister of resource-rich Sarawak since 1981, implementing ambitious plans to develop the backward state, Malaysia's largest, on Borneo island.

But he has come under fierce criticism over the years amid allegations of blatant graft, rainforest destruction, and ill-treatment of Sarawak's native tribes.

"Taib Mahmud will retire as chief minister of Sarawak with effect from February 28," Samuel Simon, a Sarawak government spokesman, told AFP.

Taib -- who has a private jet and is known for driving around in his Rolls-Royce cars -- made the widely rumoured announcement in the state capital Kuching, Simon said.

No reason for the move was given.

But Malaysia's ruling coalition has been steadily losing voter support in part due to recurring corruption scandals and allegations of poor governance, and is believed to have been pressing Taib to quit for years.

Taib's Sarawak-based party is part of the Barisan Nasional (National Front) coalition that has ruled Malaysia since independence in 1957.

Speculation is rife that Taib will continue pulling Sarawak's strings by assuming the traditionally ceremonial position of state governor.

"That can be translated to mean he still retains power," said political analyst Khoo Kay Peng.

With a population of 2.5 million people, Sarawak is crossed by powerful rivers and was once home to some of Earth's most magnificent rainforests.

Activist groups say Taib and his clan have plundered that bounty, running Sarawak like a family business by routinely awarding major government contracts to companies they control and decimating forests via logging and development of lucrative oil-palm plantations.

Taib will be replaced as chief minister by his former brother-in-law, state official Adenan Satem.

"Taib will never give up power willingly. He has too much at stake in terms of his businesses in Sarawak and his vulnerability to prosecution," said Clare Rewcastle Brown, a Sarawak-born Briton who operates the anti-Taib website, Sarawak Report.

Observers say Taib has dodged prosecution because parliament seats he controls are vital to the Barisan coalition retaining power.

The country's longest-serving chief minister, Taib has long denied allegations of improper activity.

But Swiss-based rainforest-protection group Bruno Manser Fund, citing financial documents, said in 2012 that Taib's family controlled Sarawak's biggest companies and stakes in hundreds of corporations in Malaysia and abroad.

Though Sarawak is one of Malaysia's poorest states, the fund estimated Taib's wealth at $15 billion, which would make him the richest Malaysian.

The various indigenous tribes who have traditionally dwelt in Sarawak's forests have increasingly staged protests, alleging they were being illegally run off ancestral lands.

"Taib's rule has been horrendous," said Peter Kallang, a native activist involved in a campaign to stop a series of dams being built by Taib's government.

"I am happy he is resigning but my greatest fear is that the new leader will be a Taib clone and continue his destructive polices."

Taib has pushed a campaign to build as many as a dozen hydroelectric dams -- Sarawak already has three -- in the state's wild interior, hoping cheap electricity will lure foreign industrial investment.

Tribal opponents call the dams white elephants that are inundating huge swathes of rainforest and will produce far more electricity than Sarawak needs.