It's 6 p.m. in rural Borneo and Iban tribesman Luang Anak Entiyang springs up to fetch his short-wave radio, tuning in the day's broadcast of Radio Free Sarawak for a dozen fellow villagers.

Daylight melts away into the rainforest outside and the men of Menyang village sit on the floor of Luang's simple home, leaning in to hear as callers commiserate over alleged government-backed grabs of indigenous lands.

The programme they are listening to has become so popular that authorities have threatened to jam it, activists and Malaysia's opposition are handing out thousands of radios, and villages now plan their evenings around it.

"I think we would die without RFS," Luang, 61, said of the two-hour broadcast.

"We used to eat dinner at this time, but now we listen to the radio first."

It's a scene that locals and activists say is repeated nightly in villages across Sarawak, where tribal communities in Malaysia's most resource-rich state chafe at government-backed development.

In RFS's nightly call-in show, their target is increasingly Sarawak's powerful boss, Abdul Taib Mahmud, 76, who is criticised for building huge hydroelectric dams and other policies they say threaten traditional ways.

Tensions have smoldered for years but are being fanned anew by the pirate signal of RFS, broadcast from London and founded in 2010 by Sarawak-born British journalist Clare Rewcastle-Brown, a fierce Taib critic.

RFS switched last year to a call-in format. "That is what really lifted the show -- we opened up our phone lines and people have just come at us," said Rewcastle-Brown, sister-in-law of former British premier Gordon Brown.

Sarawak's media has been controlled for decades by Taib, but villagers say RFS has opened an exhilarating alternative.

"Before, all we would ever hear was how great Taib was," said Luang.

By June, Malaysia must hold national elections in which the authoritarian government in charge for 56 years faces a formidable opposition challenge.

In Sarawak -- a vast state on Borneo island of 2.5 million people, rich jungle habitats and powerful rivers -- the challenge is aimed at Taib, who has dominated Sarawak as chief minister since 1981 and is Malaysia's longest-serving state leader.

Critics accuse Taib -- known for riding around in his Rolls-Royce cars -- of massive graft, plundering once-rich timber stocks, and flooding forests and native lands with unnecessary dams.

Sarawak is among Malaysia's poorest states, but Swiss-based forest protection group Bruno Manser Fund (BMF) says Taib could be worth as much as $15 billion, which would make him one of the world's richest people.

With a close national vote seen, Malaysia's opposition alliance hopes to gain potentially decisive parliamentary seats in Sarawak, where it holds just two of 31.

Central to its strategy is RFS, which has allowed the opposition to reach out to rural areas deep in the rugged interior, circumventing Taib-controlled media.

"We want at least one radio in each village," said Baru Bian, state chief of the opposition People's Justice Party.

Callers dial a Sarawak number to be heard on air. Luang said radios have become a sought-after item, and people rush home by 6 p.m. from farming or hunting in the rainforest.

Some callers report hiking for hours to high ground for a mobile phone signal, said Rewcastle-Brown, who adds that RFS is besieged by angry calls when its signal is disrupted, a claim backed up by villagers.

Sarawak officials have shown their irritation, accusing RFS of "poisoning" native minds, and threatening to jam it.

"They are free to broadcast, but not licensed to tell lies. RFS is telling people their land will be grabbed," James Masing, Sarawak's land minister, told AFP.

Taib's office did not immediately grant an AFP interview request. He has said Sarawak's backward economy must be developed to fight poverty and rejects the graft allegations.

But BMF Executive Director Lukas Straumann said Taib's family and cronies are stealing billions from Sarawak and were the "chief culprits" in the loss of 95 percent of its original forests.

Taib, however, is vital to Malaysia's ruling coalition -- loss of his party's seats would spell its doom -- and has been spared central government scrutiny.

"He is basically untouchable," Straumann said.

Not on RFS, where Taib's policies are torn into nightly by callers who say native land rights are being trampled.

Luang's own village of Menyang, 15 kilometres (nine miles) from Indonesian Borneo, is beset by a land dispute sparked when plantation developers seized forests for logging and cultivation, manipulating native land rules with government collusion, residents say.

Village authorities deny the accusations.

Villagers last year twice blockaded access to the area and some local protest leaders were later briefly arrested.

"These forests have been ours for centuries," Luang said, gesturing at green hills scarred by the developers' clear-cutting.

"They supply our food, our medicine."

The state-linked developers recently bought out some villagers, splitting the community, he said, but adds that RFS has stiffened the resolve of holdouts.

"We thought we were alone," he said as Iban women wrapped in bright sarongs sat outside his house listening to a radio.

"But now we know people elsewhere are standing up, too."