There were unconfirmed reports at least 200 people could be dead and about 1 500 missing around Saint Bernard town in Leyte province, said Senator Richard Gordon, who also heads the Philippine Red Cross.
Rosette Lerias, the governor of Southern Leyte province, said a school building had been buried and the mud was still advancing.
"You can't find any standing structure," Congressman Roger Mercado told Reuters, quoting reports from local officials. "It's very terrible."
One survivor feared for her children.
"I felt the earth shake and a strong gust of wind, then I felt mud at my feet," Didita Kamarenta, who lives on a mountain next to one of the villages, said on radio.
"All the children, including my two children, are lost. They might have been buried."
Gordon, speaking from Geneva, said some Red Cross volunteers were at the site of the disaster but that blocked roads and cut communications lines were hindering other rescuers.
"The Philippine air force is putting together aircraft that should be loaded with people from the mining community as well as soldiers as well as other volunteer groups," he said. "Hopefully, a dog team will be able to get ahead of them there."
Southern Leyte was the scene of one of the country's worst disasters in recent years, when more than 5 000 people died in 1991 in floods triggered by a typhoon.
History of deadly storms
The Philippines is lashed by about 20 typhoons each year, including a series of storms in late 2004 that left about 1 800 people dead or missing in provinces northeast of the capital.
Sixteen people were killed earlier this week when heavy rains and flash floods hit southeastern provinces. Environmental groups blame illegal logging for making the flooding worse.
Farmers and government agencies have been warned to prepare for a stormy La Nina weather pattern that might hit the country.
La Nina features unusually cool surface temperatures in the Pacific Ocean resulting in storm surges and strong winds. The weather bureau said typhoons, floods and rains since November might be linked to the development of the pattern.Last Mod: 20 Eylül 2018, 18:16