Sixteen people are still unaccounted for on the Japanese volcano that erupted without warning, officials said Friday, on top of the 47 known to have died.

An official from Nagano prefecture, where Mount Ontake sits, confirmed press reports that there were 16 more people believed to have been on the mountain during Saturday's eruption.

The volcano continues to belch steam and poisonous fumes, making a section near the crater inaccessible.

Rescue workers have spoken of up to half a metre (20 inches) of thick, sticky ash smothering the peak, with some of those found dead half-buried, leading to fears others may be entombed.

Heavy rain Friday forced the cancellation of the recovery operation. Forecasters say a very strong typhoon looming off Japan's coast was likely to bring further rain and high winds to the area.

That could force the recovery to be put off for days, heaping anguish on the families of those still missing who are gathered at the foot of the volcano.