Gersbach and family had moved to Atoifi only six months ago

Lance Gersbach, 60, was from the Seventh-day Adventist church.

He was working alone on a building site near a mission hospital, and there are reportedly no witnesses to the killing.

The Solomon Islands has suffered serious civil unrest in recent years, due to ethnic rivalry between indigenous residents on the main island of Guadalcanal and new settlers from Malaita.

A team of detectives has flown to the Atoifi mission in the East Kwaio district on Malaita, 130km (80 miles) east of the capital, Honiara.

Local tribal chiefs have pledged full support for the investigation.

'Baffling'

Gersbach moved to Atoifi, home to about 3,000 Seventh Day Adventists, in February with his wife and two young daughters.

"Information we have is that he was beheaded with a sharp bush knife," said a police spokesman quoted by Reuters news agency.

"The whole thing is horrific and completely baffling," said East Kwaio member of parliament Alfred Sasako.

"It has taken the whole lot of us by shock and surprise.

"He was a man of very few words, you would have to be straight out of a psychiatric hospital to attack him in the way he was."

A local police officer said that the killing might be linked to local discontent about the church's expansion in the area.

"There has been some bad feelings for a long time over the land the SDA had got," he told The Australian newspaper.

Australian officials say Gersbach was working on foundations for a new shop.

A New Zealander was stabbed to death while working on a building site in Honiara last year.