Many of those rescued suffered carbon monoxide poisoning

Many of those trapped are far from the entrance to the mine and thick smoke is said to be hampering rescue efforts.

The accident occurred early on Sunday at the state-owned Chenjiashan coal mine in Shaanxi province.

Chinese mines are among the most dangerous in the world. Last month, some 150 men died in a gas explosion in Henan province.

There have not yet been any reports of casualties or the cause of the blast, which happened at about 0710 on Sunday (2310 GMT Saturday).

The official Xinhua news agency said 123 miners had escaped and earlier reports of 187 miners trapped were revised downward.

Most who escaped were working close to the entrance to the mine, and many were suffering carbon monoxide poisoning, it said.

The explosion is reported to have happened in coal pits 8km (5 miles) from the entrance.

Witnesses saw "thick smoke pouring from the mine's ventilation shafts", which was hampering rescue efforts, said a report on the website of the Communist Party's People's Daily newspaper.

Xinhua quotes mine staff at Chenjiashan as saying communications with those trapped has been lost.

China has a dismal mine safety record. A fire at an iron ore mine in Shahe city, Hebei province, claimed 68 lives only last week.

MINING ACCIDENTS IN 2004 23 Feb: 32 die in blast at Baixing mine in Heilongjiang province 3 June: Mine blast in Hebei province initially reported to kill one. Chinese media now say 14 died and 16 officials are being prosecuted for a cover-up 20 Oct: Gas explosion at Daping mine in Henan province kills 148 - believed the deadliest accident in four years 20 Nov: Fire breaks out at iron ore mine in Hebei province, killing 68 28 Nov: 170 miners trapped underground after blast in Chenjiashan mine, Shaanxi province Life cheap in China's mines

"Why do these accidents keep happening one after another?" asked an anonymous posting on Xinhua's website, Reuters reported.

"Why don't the relevant authorities do something about it? Why don't we just kill a bunch of officials? Are Chinese people's lives worth less than money?" asked the person.

Official figures show that 4,153 people died in mining accidents in China in the first three quarters of this year - a figure 13% lower than last year.

But correspondents say the total may be much higher, since many deaths go unreported.

The country's energy shortage means the price of coal has gone up, leading unscrupulous mine operators to cut corners to increase production or re-open mines which had been shut down for poor safety standards.