Mount Ontake , Japan ( CNN ) -- At least 31 people are presumed dead after rescuers found them showing no signs of life Sunday near the summit of a Japanese volcano that started erupting a day earlier . Police said the people were in a state of `` cardiac arrest , '' meaning that they were discovered without a pulse and were n't breathing but had n't been declared dead by a doctor . A coroner confirmed the first four deaths Sunday . Rescue teams had begun searching Sunday for dozens of climbers who were caught by the sudden eruption of Mount Ontake . The volcano in central Japan unleashed a huge cloud of ash late Saturday morning that billowed down the mountainside and engulfed hikers in its path . Witnesses described hearing a sound like thunder when the eruption began . The exact number of people unaccounted for was unclear , as officials were uncertain how many had already made it off the mountain . Desperate relatives . Relatives of the missing gathered near Mount Ontake on Sunday desperately seeking information . Among them was Kiyokazu Tokoro from nearby Aichi prefecture , whose son , Yuki , was hiking on the volcano with his girlfriend . He said he knew they were near the summit at the time of the eruption because his son 's girlfriend had sent a photo to a friend minutes beforehand . `` All I can do is beg for your help to get information , '' he told CNN . `` Please help us . '' Authorities estimated there were 200 to 250 hikers in the area at the time of the eruption . Most of them were reported to have managed to make the long trek down the mountain . But some people remained trapped in several lodges on Mount Ontake , and others were missing altogether , local authorities said . More than 350 rescue workers -- a mix of police , firefighters and military personnel -- began climbing two separate routes up the mountain on Sunday morning , authorities in the nearby village of Otaki said . Alert level raised . Aside from those in cardiac arrest , more than 25 people were reported to have been injured , 10 of them seriously , according to the government of Nagano prefecture , where the volcano is situated . Helicopters ferried some injured people off the mountainside . Among the climbers trapped in the cottages , at least 11 were injured , officials in Otaki said . They said they had observed 17-20 inches ( 40-50 centimeters ) of volcanic ash covering the ground in some areas . The Japan Meteorological Agency has raised the Volcanic Alert Level for Ontake from 1 to 3 . That means the public is advised to not approach the volcano , the summit of which is at an altitude of 10,060 feet ( 3,067 meters ) . The agency warned that another large eruption could take place in the next six days or so . Small continuous eruptions continued Sunday . The volcano 's plume of smoke and ash was reported to have disrupted air travel in Japan , causing delays at several airports . Popular destination . Mount Ontake , the second tallest volcano in Japan , after Mount Fuji , is a popular destination for hikers , especially in the fall when the foliage 's rich autumn colors are on display . About 250 people living near the mountain have decided to remain in their homes , police said . The last major eruption of Mount Ontake , which is about 125 miles ( 200 kilometers ) west of Tokyo , took place in 1979 , according to the Global Volcanism Program at the Smithsonian Institute . That eruption lasted months , spewing out more than 200,000 tons of ash , the Japanese news agency Kyodo reported . Smaller scale activity was reported in 1984 , 1991 and 2007 . CNN 's Will Ripley reported from Mount Ontake , and Jethro Mullen reported and wrote from Hong Kong . CNN 's Junko Ogura contributed to this report .
TV : ` ` Please help us , '' cries a father seeking information on his missing son . At least 31 people are found on the mountain in a state of ` ` cardiac arrest , '' police say . Seismologists predict that another big eruption will take place in the coming days . Mount Ontake is erupting Saturday , unleashing a cloud of ash that attracts hikers .