The death toll from Japan's worst volcanic eruption in decades is likely to rise to around 46 after as more victims were discovered on the ash-covered summit, media said on Wednesday.

Military searchers resumed a recovery operation with helicopters early on Wednesday after poisonous gas and fears of further eruptions on Mount Ontake led officials to cancel rescue efforts a day earlier.

The eruption of the 3,067-metre (10,062-foot) peak, 200 km (125 miles) west of Tokyo, blanketed the peak with a deadly rain of ash and stone as the hiking site was packed with climbers, including children.

Military personnel discovered around 10 victims in a state of cardiopulmonary arrest on Wednesday, several domestic television stations reported. Japanese authorities are highly likely to wait until the victims have been brought off the mountain and examined by a doctor before declaring death.

The police for Nagano Prefecture, which is where half of the mountain is located, said they could not confirm the reports.

If confirmed dead, that would add to the 36 other people also feared to have died on Mount Ontake.

Volcanoes erupt periodically in Japan, one of the world's most seismically active nations, but there have been no fatalities since 1991, when 43 people died in a pyroclastic flow, a superheated current of gas and rock, on Mount Unzen in the southwest of the country.

If the death toll on Mount Ontake rises above 43, it would be the most lethal volcanic eruption since 1926, according to data on the Japan Meteorological Agency's website.

Mount Ontake, Japan's second-highest active volcano, last had a minor eruption seven years ago. Its last major eruption, the first on record, was in 1979.

Hikers said there was no warning of Saturday's eruption just before noon and hundreds were trapped for hours before descent became possible later in the day.