Indonesia has blocked internet access in the province of Papua over fears that a stream of offensive and racists posts online will spark more violent protests in the region, the government has said.

Riots and demonstrations brought several Papuan cities to a standstill this week, as buildings were torched and street battles broke out between police and protesters in Indonesia's easternmost territory.

A rebel insurgency against Jakarta's rule has simmered for decades in the island region, which shares a border with Papua New Guinea.

But the riots appear to have been triggered by the arrest of dozens of Papuan students, who were also pelted with racist abuse, in Java at the weekend.

Indonesia slowed internet service in recent days to clamp down on hoaxes, provocative comments and racist abuse targeting Papua's ethnic Melanesian population, but it shut down service completely late last night.

"As of this morning, there is still a full block on internet access," said Indonesia's communications ministry spokesman, Ferdinandus Setu.

"The amount of racist and provocative content online was very high ... and it went viral."

The region's three internet providers cooperated with the shutdown, but many users managed to get around the block, Mr Setu said.

"The restrictions have not been that effective," he added.

"We're still evaluating the situation ... and will probably lift the block by this afternoon if possible."

Calm appeared to have been mostly restored today after Indonesia sent in 1,200 extra police and military to Papua, with some 45 protesters reportedly arrested.