A tour bus veered off a road in the central Japanese town of Karuizawa, January 15, 2016. [Photo/IC]

TOKYO - The death toll of a tour bus crash in Japan's central Nagano Prefecture early Friday has risen to 14, according to the latest local media reports.

Japan's top government spokesperson Chief Cabinet Secretary Yoshihide Suga told a press conference that 14 people had lost their lives among the 41 people traveling on the bus that was headed to a popular ski resort in Nagano.

Thirty nine of those on the bus were passengers and two were drivers, local rescue officials said.

The latest reports said around 30 people had been injured and were being treated in hospital, with 6 people in critical condition. Public broadcaster NHK reported the critically injured were showing "no vital signs" with fears mounting that the death toll may rise further.

The accident occurred at around 2 am local time Friday (1700 GMT Thursday) on National Route 18, about 2 km south of the JR Karuizawa station.

Police and investigators confirmed that the road conditions were not icy and investigations into the cause of the accident were underway.

The tour bus departed from Shinjuku in central Tokyo on Thursday night, local media said. It veered onto the opposite lane of the road, before hitting a guard rail and flipping over.

The tour bus full of skiers on its way to the Kitashiga highlands in the northern part of Nagano, ended up on its side in a wooded ravine off a mountainous road between Nagano and Gunma prefectures.

The emergency call to rescue services was made by one of the passengers, according to the local media.