Safety officials and investigators have blamed poor management and inadequate safety precautions for the coal mine blast that has claimed 104 lives so far in northeast China's Heilongjiang Province.

As of 2:30 a.m. Monday, four miners remained trapped at Xinxing Coal Mine under the state-owned Heilongjiang Longmei Mining Holding Group's subsidiary in Hegang City.

Luo Lin, head of the State Administration of Work Safety (SAWS), said Monday the accident started with a gas leak in one of the shafts. But as a result of poor ventilation, gas quickly poured into the main tunnel and triggered an explosion that shook 28 of all the 30 mining platforms in operation.

He said management of the mine were to blame for failing to evacuate the workers promptly after an extraordinarily high gas density was detected in the pit.

"Investigators are yet to determine the exact cause of the accident after a thorough probe at the site," said Luo.

"The accident has again revealed many problems in colliery management -- it's a lesson we must all learn."

A total of 528 miners were working in the pit when Fan Minghua's gas detector beeped at 1:37 a.m. Saturday. "I manually tested the gas density in the air, which read over 10 percent," said Fan, who has monitored gas density in the pit for four years.

Safety regulations rule that all miners must be evacuated when gas density exceeds 2 percent.

Fan shouted for everyone on his platform to escape, shut off the power and informed coordinators on the surface. He contacted other gas monitors, who together helped dozens of miners to flee.

Realizing that the nearest route to escape had been blocked by toppled equipment, gas monitor Wang Shili left a message on the wall with a chalk, "Dead end here. Exit from Northern Tunnel."

When miner Wang Naihui saw thick yellow smoke billow into the air, he immediately covered his mouth and nose with his towel. He poured some water on the face of his co-worker Lin Maohai who had fainted and dragged him out of the pit.

At a press conference Monday, journalists demanded an explanation as to why management of the mine failed to evacuate more people in the one hour between Fan's report and the blast. Mine official Zhang Jinguang, however, insisted evacuation was "timely."

"But evacuation took time and the miners had to run a long way from their mining platforms to the surface," said Zhang.

But inadequate precautions and poor ventilation were apparently among the fatal failures, said Zhao Tiechui, deputy head of SAWS.

"The mine has too many mining platforms in operation and has sent too many workers down the pit to increase output," Zhao said Sunday. "Its underground structure, however, is far too complicated for its current ventilation system to work effectively."

Rescue work continued Monday for the four missing miners.

Sixty-five people were injured in the accident. Most of them suffered gas poisoning, burns, fractures and bruises. The provincial health authority has sent four psychologists to provide counseling.