Turkey's prime minister said Wednesday that 232 people are confirmed dead from an explosion at a mine, as rescuers battled to reach potentially hundreds still trapped in one of the country's worst ever industrial disasters.

Recep Tayyip Erdogan arrived to inspect the site in the western town of Soma, in Manisa province, where an electrical fault caused an explosion the previous day, leading parts of the mine to collapse.

Most of the deaths have been caused by carbon monoxide poisoning. Three days of national mourning have been declared.

Meanwhile, Turkish police fired tear gas and water cannon at around 800 protesters in Ankara who accused the government and mining industry of negligence.

The protesters, mostly students, hurled stones at the police and shouted anti-government slogans as they tried to march from a university in Ankara to the energy ministry, an AFP photographer said.

Fires and toxic gases were complicating the rescue effort by 400 workers, said Energy Minister Taner Yildiz.

"I must say that our hopes about rescue efforts inside (the mine) are fading," he added.

It is not clear how many remain trapped in the mine. Nurettin Akcul, head of Turkey's mining union, told AFP there were between 100 and 150 people.

The miners are all thought to have gas masks, but it was not clear how long they would last.

Earlier reports said 787 workers were underground when the blast occurred. Yildiz said 363 had been saved as of early Wednesday.

Only a handful of miners were seen pulled from the collapsed mine on Wednesday morning, many of them already dead, an AFP reporter at the scene said. One emerged wearing an oxygen mask and was immediately rushed to hospital.

As victims were taken away on stretchers, friends and relative desperate for news of their loved ones tried to pull away the sheets covering their corpses.

Most sat silently on benches, their faces blank with shock, while others scoured a list of the wounded posted up on a wall alongside the name of the hospital they were taken to.

One young woman, Bahar Galici, stared at the sheet of paper before walking away. "Still nothing," she sighed.

Harun Unzar, a colleague of the missing miners said he had lost a friend previously "but this is enormous."

"All the victims are our friends," he said as he wept.

"We are a family and today that family is devastated. We have had very little news and when it does come it's very bad," he added.

A security source told AFP there were pockets in the mine, one of which was open so rescuers were able to reach the workers, but the second was blocked with workers trapped inside.

Fire officials were trying to pump clean air into the mine shaft for those who remained trapped some two kilometres (one mile) below the surface and four kilometres from the entrance.

'Tragic accident'

Explosions and cave-ins are common in Turkey, particularly in private mines, where safety regulations are often flouted.

Turkey's worst mining accident happened in 1992 when 263 workers were killed in a gas explosion in a mine in northern Zonguldak.

A lawmaker from the main opposition Republican People's Party (CHP) said it submitted a parliamentary motion 20 days ago to investigate work-related accidents at coal mines in Soma but it was rejected by the government.

The CHP's Manisa deputy Ozgur Ozel told local media: "We receive tip-offs every day that workers' lives are under threat.

"We lawmakers from Manisa are tired of going to miner funerals."

Tuesday's explosion was believed to have been triggered by a faulty electrical transformer at around 1230 GMT.

Turkey's ministry of labour and social security said the mine was last inspected on March 17 and was found to comply with safety regulations.

But Oktay Berrin, a miner, said workers were not protected underground.

"There is no security in this mine," he told AFP.

"The unions are just puppets and our management only cares about money."

'Heartfelt condolences'

Cemile Dag, a woman in her 50s, said she had been waiting since Tuesday afternoon for news of three relatives trapped underground, including her grandson and her nephew.

"All three were working in the same pit... I couldn't get any news on the telephone so I came here," she said.

Energy Minister Yildiz promised the government would "not turn a blind eye" to negligence. "We will do whatever necessary, including all administrative and legal steps," he said.

The mining company Soma Komur said it had taken maximum measures to ensure safety.

"The accident happened despite maximum safety measures and inspections, but we have been able to take prompt action," it said.

Erdogan and President Abdullah Gul both cancelled foreign trips to travel to Soma.

Erdogan expressed his "heartfelt condolences" to the families of those who died.

"Some of the workers have been rescued and I hope we will be able to rescue the others," he said in Ankara.

France, Germany and the European Union all offered their condolences and assistance.

"It is with shock that I learned the news of this grave mining catastrophe. Germany is by the side of your country as this difficult time and is ready to help," said German Chancellor Angela Merkel.

Soma is a key centre for lignite coal mining around 250 kilometres (150 miles) south of Istanbul.