Japan called for calm but braced for trouble with tight security yesterday, as low-key protests began ahead of its leg of the Olympic torch relay, following emotional scenes at other venues around the world.

The global torch relay ahead of the Beijing Games in August has provoked protests against China's rights record, especially in Tibet, as well as patriotic rallies by Chinese who say the West has vilified Beijing unfairly.

The flame is meant to transmit a message of peace and friendship, but its journey has been largely turned into a political event and the torch has been granted the sort of security usually reserved for state leaders.

Chief Cabinet Secretary Nobutaka Machimura called for calm ahead of today's relay in the central Japanese city of Nagano, a former Winter Olympics site.

"I hope this torch relay will take place peacefully in an atmosphere where everyone can celebrate," he said.

The torch will be guarded by up to 4,000 police, media said, with riot police and another 100 regular officers set to shield torch-bearers in two rows, shrouding the runners from sight.

They will be joined by two Chinese "flame attendants", although Japan has made it clear that their participation in security would not be welcome after criticism of the paramilitary guards as heavy-handed in protecting the torch elsewhere.