Farmers and activists concerned about soaring food prices and global warming are gathering for a demonstration in Hokkaido's main city of Sapporo.

The summit venue in a remote lakeside resort has been sealed off by thousands of police.

Previous G8 summits have been marred by clashes between police and protesters.

To protect the leaders from the G8 - Britain, Canada, France, Germany, Italy, Japan, Russia and the US - about 21,000 police have been deployed.

Summit organisers are keeping protesters and journalists well away from the summit itself, in the resort of Toyako.

Some people hoping to attend the summit, including activists, academics and independent journalists, have complained that they were questioned at length on entering Japan.

The security budget for this year's summit is said to be more than $280m (£140m), far higher than the year before, says the BBC's Tokyo correspondent Chris Hogg.

Exclusion zone

Demonstrators have begun to gather in camps outside the security exclusion zone.

Japanese farmers and other demonstrators in Sapporo have begun what is expected to be a major rally ahead of the summit.

Some of the activists are concerned about global warming and the steep rises in the price of food in recent years and want the G8 leaders to take action.

A campaigner for Oxfam International said that the leaders should concentrate on finding solutions.

"This isn't the time for a holiday, this is the time for sorting out problems," said Lucy Brinicombe.

Meanwhile, British PM Gordon Brown has said the G8 must commit to united actions to tackle poverty and climate change and must not retreat into isolationism.

"Instead of sidelining climate change and the development agenda, the present economic crisis means that instead of relaxing our efforts we have got to accelerate them", he told the Guardian newspaper.

BBC