More than 30 hikers were found unconscious and in "cardiac arrest" Sunday near the peak of an erupting volcano, police said, employing a term typically used by Japanese authorities before doctors are able to certify death officially.

Rescue workers found the individuals near the summit of 3,067-metre (10,121-foot) Mount Ontake, which erupted around noon on Saturday.

"We have confirmed that more than 30 individuals in cardiac arrest have been found near the summit," a Nagano prefecture police spokesman told AFP without elaborating further.

Nagano prefecture posted on its website that about 30 people had heart and lung failure, the customary way for Japanese authorities to describe a death until police doctors conclude their examinations.

Before the unconscious victims were found, Japan’s Fire and Disaster Management Agency said that 45 people had been reported missing.

Mount Ontake in central Japan erupted shortly before noon on Saturday, spewing large white plumes of gas and ash high into the sky and blanketing the surrounding area in ash. The mountain is a popular climbing destination, and at least 250 people were initially trapped on the slopes, although most made their way down by Saturday night.

Some 550 soldiers, police officers and firefighters were involved in a large-scale search-and-rescue operation in a bid to save dozens of hikers who were thought to have been stranded on the volcano when it erupted without warning, spewing ash and steam into a sunny autumn sky.

A suffocating blanket of ash up to 20 centimetres (eight inches) deep covered a large area of the volcano, forcing up to 150 to seek refuge in mountaintop shelters at one point.

Local officials believe 45 to 49 hikers sheltered overnight in cabins on the mountain, which is particularly popular among hikers in late September as the leaves change colour for autumn.

(FRANCE 24 with AFP and AP)