Jakarta – Logging and forest fires are destroying rainforests and the wildlife they support, government authorities and environmentalists warned yesterday.

Uncontrolled forest fires – mostly lit illegally to clear logged forest areas for palm oil plantations – are again raging through Borneo and Sumatra, while a blanket of smoke is covering villages and towns on the islands. The fires were mostly lit by plantation companies taking advantage of a three-month drought, the state-run Antara news agency said.

Local authorities feared a repeat of the huge rainforest fires of recent years, in which "millions of hectares of tropical forest were destroyed" on Borneo and Sumatra, Antara said.

Environmental groups warned in Jakarta that large-scale illegal logging in two Indonesian national parks seriously threatened the survival of orang-utans, one of the world's most endangered species.

The Environmental Investigation Agency, based in London and Washington, and Telapak Indonesia said illegal logging was rampant in the Gunung Leuser National Park in North Sumatra and the Tanjung Puting National Park in central Kalimantan.

"I have witnessed scenes of appalling devastation in both of these so-called protected parks. The logging is totally out of control," said agency director Dave Currey. "The Government of Indonesia must act against the timber barons directing this destruction before these vital areas and their wildlife are lost."

The Gunung Leuser National Park in northern Sumatra covers 2.5 million hectares, from the Indian Ocean to the hills along the Straits of Malacca, and has mountains 3,000 metres high.

Unlike orang-utans elsewhere, the ginger-haired primates in the park's Suaq Balimbing region live in structured social groups and make and use tools, the agency said. Yet activists had "witnessed loggers with chainsaws operating in the Suaq Balimbing research area".

The Tanjung Puting National Park on Borneo – where an orang-utan research programme was set up in the early 1970s – was also under great threat from illegal logging. "We are calling for the Indonesian Government to clamp down immediately on the illegal logging," the groups said.

"We are also calling for the international community to use their power within Indonesia to try to get the Government to act.

"If we don't see this happening soon, both Tanjung Puting National Park and Gunung Leuser National Park will no longer be worth protecting and some of these species, especially orang-utans, may be lost forever."