Thousands of troops and rescue workers are battling flooding and landslides after the strongest typhoon to hit Japan in 60 years.

The storm has killed around two dozen people, with more still missing according to public broadcaster NHK.

In central Nagano prefecture, water surrounded Japan's famous bullet trains while helicopters plucked stranded residents from rooftops.

A total of 27,000 military troops and other rescue crews have been deployed in relief operations, authorities said.