Japan volcano: Bid to reach hikers on Mount Ontake
As the rescue effort resumed on Sunday, more than 500 Japanese soldiers and police headed for the area.
"It's very hard to know what's happening on the mountain now and things could change," said one official with the government of Nagano prefecture, quoted by Reuters.
A spokesman at Otaki village said a military helicopter surveying the summit had rescued a man and a woman.
"It found the two people waving at it," the spokesman told AFP news agency.
"Originally, the rescuers thought it might be difficult to go near them because ash could rise (and damage the helicopter), but the conditions were better than they believed," he added.
Video footage posted online showed hikers scrambling to descend as ash and steam enveloped them.
"All of a sudden ash piled up so quickly that we couldn't even open the door," Shuichi Mukai, who worked in a mountain hut just below the peak, told Reuters.
He said the hut quickly filled with hikers taking refuge.