Indian authorities said Thursday that it may take "some days" to recover the body of an American killed in a hail of arrows shot by a tribe untouched by modern civilisation.

John Allen Chau, 27, was attacked as he set foot last week on the remote North Sentinel Island, one of the Indian Andaman Islands in the Bay of Bengal that is off limits to visitors, according to police.

Dependra Pathak, the head of the region's police, told AFP that authorities sent a helicopter to the area and then a ship to identify where the incident took place.

"We maintained a distance from the island and have not yet been able to spot the body. It may take some more days and... (reconnaissance) of the area," Pathak added.

North Sentinel is home to the Sentinelese people, believed to number only around 150. To protect their way of life, foreigners and Indians are banned from going within five kilometres of the island.

Police have roped in field experts including Indian anthropologists, and tribal welfare and forest officers to help them tackle the situation.

"We have to take care that we must not disturb them or their habitat by any means. It is a highly sensitive zone and it will take some time," Pathak said.

Indian police said a murder case had been registered against "unknown" tribespeople and that six fishermen and one other person who allegedly helped Chau get to the island were arrested.

Authorities said one of the objectives of the arrests was "demonstrative effect, so that entire world and locals know that no one can go there."