Rescuers desperately searched for signs of life on Saturday after a methane blast at a coal mine in northern Turkey killed at least 40 people and trapped dozens of others hundreds of metres underground.

Updating the death toll, Health Minister Fahrettin Koca also tweeted that 11 others pulled out alive were being treated in hospital after one of Turkey's deadliest industrial accidents in years struck Friday at sunset.

"We are facing a truly regretful situation," Interior Minister Suleyman Soylu told reporters earlier after urgently flying to the small coal mining town of Amasra on Turkey's Black Sea coast.

"In all, 110 of our brothers were working (underground). Some of them came out on their own, and some of them were rescued."

Soylu also confirmed early reports that nearly 50 miners remained trapped in two separate areas between 300 and 350 metres (985 to 1,150 feet) below ground.

Television images showed anxious crowds -- some with tears in their eyes -- congregating around a damaged white building near the entrance to the pit in search of news for their friends and loved ones.

Turkish President Recep Tayyip Erdogan said he would cancel all his other arrangements and fly to the scene of the accident on Saturday.

"Our hope is that the loss of life will not increase further, that our miners will be found alive," Erdogan said in a tweet.

"All of our efforts are aimed in this direction."

Most initial information about those trapped inside was coming from workers who had managed to climb out relatively unharmed.

But Amasra mayor Recai Cakir said many of those who survived suffered "serious injuries".

The blast occurred moments before sunset and the rescue effort was being impeded by the dark.

Turkey's Maden Is mining workers' union attributed the blast to a build-up of methane gas.

But other officials said it was premature to draw definitive conclusions over the cause of the accident.

- 2014 disaster -
Rescuers sent in reinforcements from surrounding villages to help search for signs of life.

Television images showed paramedics giving oxygen to the miners who had climbed out, then rushing them to the nearest hospitals.

The local governor said a team of more than 70 rescuers had managed to reach a point in the pit some 250 metres below.

It was not immediately clear if the rescuers would be able to come any closer to the trapped workers or what was blocking their further passage.

Turkey's AFAD disaster management service said the initial spark that caused the blast appeared to have come from a malfunctioning transformer.

It later withdrew that report and said methane gas had ignited for "unknown reasons".

The local public prosecutor's office said it was treating the incident as an accident and launching a formal investigation.

Turkey suffered its deadliest coal mining disaster in 2014 when 301 workers died in a blast in the western town of Soma.