Man-eating bears kill two scientists and lay siege to survivors trapped in remote forest base

The team of geologists on the Kamchatka Peninsula were forced to remain in camp with weapons ready as the ravenous bears - some ten feet tall - roamed around outside.

The bears are thought to have run out of their normal diet of fish and smaller animals - and to have turned instead to hunting humans.

A brown bear in Kamchatka, as pictured in the winning Shell Wildlife Photographer animal portrait last year

A spokesman for the Emergency Situations Ministry said: 'The people inside are scared by the invasion of bears. The bears are hungry - for some reason there is not enough food for them this summer.'

A massive brown bear killed two geologists at their work site on Friday. They were trapped in open ground and the 1,500 lb bear outran and killed them.

It is feared that the same bear is among those now threatening the beleaguered party of scientists.

Officials in Kamchatka said that this year was remarkable for either too many bears or not enough fish.

Rampant fish-poaching in the tundra sends hungry bears into populated centres each year, attracted to the garbage humans leave behind.

But is rare for a group of bears to encircle an encampment for a prolonged period of time.

Three people in the area die on average annually from bear attacks.

Hunter: The bears, which weigh up to a quarter of a ton, are thought to be ravenous after running out of food

But three have died in three weeks this summer and experts believe the bears are becoming increasingly desperate.

The two geologists killed last week were found in a remote wilderness area where they had been working for a local mining company.

Locals who found the body said: 'They were in the open. The bears can run faster than humans. They didn't stand a chance.'

Last month a student taking part in an orienteering race was pursued and killed by a bear, probably as she disturbed the female with a cub. The bear also chased and nearly killed another runner.

The Kamchatka brown bear is one of the world's largest bear species, weighing around 110 stone  - nearly three quarters of a ton - and with a body length of up to 10 feet.

Around 16,000 bears inhabit the region but Russia's agricultural regulator Rosselkhoznadzor says the local bear population is on the rise.

Officials said a helicopter ferrying officials and hunters could not fly in bad weather, but an all-terrain vehicle was on its way to the camp, where its crew would await government approval to shoot the bears.