Relatives of one of the 29 miners and contractors trapped in the Pike River Mine leave a meeting in Greymouth November 20, 2010. New Zealand rescuers have yet to make contact with 29 trapped miners as fears of lethal gas levels prevented any chance of a rescue on Saturday, 24 hours after an explosion ripped through the remote colliery dug into the side of a mountain. [Xinhua/Reuters]

Rescue efforts at New Zealand South Island West Coast's Pike River coal mine continued to be hampered on Sunday as air samples taken from the mine indicate there is still a risk of further explosions.

Pike River chief executive Peter Whittall said at a press conference on Sunday that a rig will attempt to drill 150 meters into the Pike River mine to take air samples.

He expects the drilling to break through on Sunday evening.

Twenty-nine men remained trapped in the coal mine following a large explosion at the site on Friday afternoon.

Whittall said tests showed that there was some combustion of material in the mine generating heat and gases, including the poisonous carbon monoxide.

Whittall said the gas levels in the mine were reducing, rather than increasing, but the tests suggested the situation was still unsafe to send in a rescue team.

The police officer in charge, Gary Knowles, reiterated on Sunday it is still a rescue operation but emergency workers could not enter the mine while it was still unsafe.

The quality of oxygen being extracted from the mine was still high, said Knowles.

There was still a compressed air line pumping oxygen somewhere along the shaft where the 29 miners are trapped, he said.

The most recent air samples were taken from the mine around 8 p. m. Saturday and showed levels of potential explosive. Testing will resume on Sunday.

Family members of the workers will be transported to the mine on Sunday to help them understand the situation there. Access has been restricted since the explosion.

Two men walked out of the mine unaided on Friday and have been discharged from hospital.

The other workers are believed to be trapped about 2km along the horizontal tunnel burrowed into the side of a mountain about 150 meters below the surface. Their conditions are not known.

Sixteen of the workers are employed by Pike River Coal, while 13 are local contractors. The youngest of the miners is a 17-year- old New Zealander, while the oldest is 62.

Police have confirmed the nationalities of the workers. There are 24 New Zealanders, two Australians, two British citizens and one South African.

A sizable team of Australian mine safety experts and equipment have arrived in New Zealand.