Indonesian authorities say independence supporters in the restive province of Papua have slaughtered up to 31 people who were working at a state-owned construction company.

Key points: The alleged separatist attack is the worst for many years in Indonesia's Papua region

The alleged separatist attack is the worst for many years in Indonesia's Papua region The violence reportedly flared after migrant workers photographers a pro-independence rally

The violence reportedly flared after migrant workers photographers a pro-independence rally A low-level insurgency has plagued the mineral-rich but impoverished region for decades

Papua police spokesman Suryadi Diaz said 24 workers were killed when gunmen stormed a government bridge construction project in a remote mountainous village in Nduga district.

Eight other workers fled to the nearby house of a local Parliament member, but an armed group came a day later and killed seven of them, Mr Diaz said, citing reports from several witnesses. One managed to escape and remains missing.

"This is the worst attack launched by the armed criminal group recently amid intensified development by the Government," Mr Diaz said.

He said security forces were trying to recover all 31 bodies but they were scattered and guarded by gunmen in the district, a stronghold of separatists who have battled Indonesian rule for more than 50 years.

For years, a low-level insurgency has plagued the mineral-rich but impoverished region, which is ethnically and culturally distinct from much of Indonesia.

Papuan activists held multiple rallies on Saturday to commemorate what they regard as their independence day from Dutch colonial rule. ( AP: Trisnadi )

Papua, a former Dutch colony in the western part of New Guinea, was officially incorporated into Indonesia in 1969 after a United Nations-backed ballot that was widely criticised as a sham.

Local media reports said the violence flared after the workers angered pro-independence supporters by taking photographs at a rally on Saturday.

Some Papuans regard December 1 as their independence day from Dutch colonial rule, raising a banned separatist flag and holding rallies.

Minister of Public Works and People's Housing Basuki Hadimuljono told a media briefing in Jakarta that the victims were among dozens of construction workers employed by a state-owned construction company to build bridges along a 278-kilometre road project connecting the towns of Wamena and Agats.

The workers, migrants from other parts of Indonesia, are considered outsiders by the separatists.

The Government, which for decades had a policy of sending Javanese and other Indonesians to settle in Papua, is now trying to spur economic development to dampen the separatist movement.

Indonesia's human rights commission has also urged President Joko Widodo to end rights violations by security forces in Papua, an area where access by foreign media is restricted.

Sorry, this video has expired Five key things to know about West Papua ( Del Irani )

ABC/wires