Timika – Gunmen using military-issue weapons pre-planned an ambush that killed an Australian mine worker in Indonesia's restive Papua province, police have said.

Drew Grant, 38, who worked for the Indonesian subsidiary of US-based mining giant Freeport McMoRan, was shot dead as he travelled in a car with three others on a road between Tembagapura and Timika, Papua police chief Bagus Ekodanto told reporters in Timika late Saturday.

"The shooting was pre-planned. (It's) clear they (the attackers) were using weapons belonging to the police or the military," he added.

The attack occurred in Freeport's vast concession area, which includes the massive Grasberg gold and copper mine. Police are still investigating the number of attackers involved and their motive for killing, Ekodanto said.

"He (Grant) was shot five times in the neck, chest and stomach from a distance of 25 metres. We're still investigating the case. We don't want to be hasty and say they are from separatist groups," he added.

Freeport Indonesia is the largest single taxpayer to the Indonesian government. Grasberg sits on the world's largest gold and copper reserves on the far eastern extreme of the Indonesian archipelago.

Pro-independence militants have waged a long-running insurgency against Indonesian rule in Papua, which is off-limits to foreign journalists without special permission.