GUINSAUGON, Philippines – Rescue workers refused to give up hope of finding survivors in an elementary school buried by up to 100 feet of mud, digging into the night Monday after detecting what the provincial governor called “signs of life.”

Sounds of scratching and a rhythmic tapping were picked up by seismic sensors and sound-detection gear brought in by U.S. and Malaysian forces.

“To me, that’s more than enough reason to smile and be happy,” South Leyte Gov. Rosette Lerias said. “The adrenaline is high … now that we have seen increasing signs of life.”

Still, it was hard to imagine survivors under the wet muck nearly four days after a mountainside collapsed and covered the farming village of Guinsaugon, killing up to 1,000 people. No one has been pulled out alive since just a few hours after the disaster Friday morning.

The search has focused on the school because of unconfirmed reports that some of the 250-300 children and teachers may have sent cell phone text messages to relatives soon after the disaster.

Under the glare of generator-powered lights, a multinational group of troops and technicians used high-tech gear like seismic sensors and sound- and heat-detection equipment alongside shovels and rescue dogs. They finally halted about 3 a.m. Tuesday until daybreak.

A U.S. military spokesman said late Monday that U.S. Marines digging at the site had found bodies, but no survivors.

“I asked had they received or found any type of survivors, and the answer was no,” U.S. Marine Capt. Burrell Parmer said after speaking to the commander of U.S. forces at the disaster site.

The statement discounted an earlier report by Philippine Interior Undersecretary Marius Corpus that U.S. Marines had found 50 survivors. There was no immediate explanation for how the false report had spread.

“There is a lot of rubble, a lot of large boulders,” Parmer said. “On some sides near the river, it’s very moist, very soft soil, and you can get stuck up to … your waistline if you’re not careful.”

Still, the Marines were eager to discover the origin of sounds detected by seismic sensors.

“The farther down we went, the signals grew stronger,” U.S. Marine Lt. Richard Neikirk said as he pointed to a spot under a big boulder.

A Malaysian team using sound-detection gear picked up noises, too.