Rescue crews waited impatiently outside one of New Zealand's largest coal mines Friday night for the all-clear to begin a search for 27 men missing after a powerful gas explosion struck deep underground.

Five dazed and slightly injured miners stumbled to the surface hours after the blast shot up the 360-foot- (110-meter-) long ventilation shaft. Video from the scene showed blackened and singed trees and light smoke billowing from the top of the rugged mountain where the mine is located, near Atarau on New Zealand's South Island.

Fears that pockets of methane gas remained and could ignite held up the rescue attempt, and it could be days before it was safe enough for specialist teams to enter the mine, said Tony Kokshoorn, mayor of nearby Greymouth.

Electricity went out shortly before the explosion and that failure may have caused ventilation problems and contributed to a buildup of gas. The power outage complicated efforts to pump fresh air into the mine and make it safe for rescuers to enter.

"They're itching to get in there and start looking for other people and a bit frustrated at having to stand and wait," said police spokeswoman Barbara Dunn. "There is concern that ventilation inside the mine shaft may be compromised by the power outage."

Teams were preparing for a rescue bid Saturday at the mine, but it remained unclear when the operation would begin.

While the condition of the missing miners was unknown, the prospect that they could be alive but trapped recalled the dramatic saga of 33 Chilean mine workers who spent 69 days a half-mile (less than a kilometer) deep in a collapsed gold and copper mine. Their rescue last month played out on live television that captivated the world.

"We are holding on to hope," Kokshoorn told reporters. "Look at Chile, all those miners were trapped and they all came out alive."

John Dow, chairman of mine operator Pike River Coal Ltd., said each miner carried 30 minutes of oxygen _ enough to reach oxygen stores in the mine that he said would allow them to survive for "several days."

The coal seam at the mine is reached through a 1.4-mile (2.3-kilometer) horizontal tunnel that bores into the mountain toward the seam, which lies about 650 feet (200 meters) beneath the surface. According to the company's website, the vertical ventilation shaft rises 354 feet (108 meters) from the tunnel to the surface.

Kokshoorn said it was unclear at what depth the explosion happened but that the blast was very large. He put the number of miners unaccounted for at up to 30. Peter Whittall, Pike River Coal's chief executive, said 27 were missing _ 15 miners employed by the company and 12 local contractors.

Pike River spokesman Dick Knapp confirmed late Friday the mine had been rocked by a gas explosion, but said its cause was still unknown. It also was not clear if all of those underground were together.

Whittall said five workers had walked out of the mine two to three hours after the blast: a pair that included the machine operator who was blown off his vehicle one mile (1.5 kilometers) into the access tunnel, and three others who came out later. One of the men had been able to make a call on his cell phone before reaching the surface, he said.

New Zealand Prime Minister John Key said the situation at the mine had the potential to be very serious.

"The government has told the company it will provide any support that is required. It is an Australian company that owns the mine and the Australian government has also contacted us offering their support (and) assistance," he told reporters.

Pike River Coal is a New Zealand-registered company, but its majority owners are Australian. There are also Indian shareholders.

Energy Minister Gerry Brownlee said the explosion happened about 3:45 p.m. (0245 GMT Friday, 9:45 p.m. EST Thursday), and the last contact with any of the miners was about half an hour later. They had not spoken to any of the missing miners in that time.

Two of the men who came to the surface were taken to a hospital for treatment of minor injuries.

"They're being interviewed and we're trying to determine ... the full nature of the incident," Whittall said.

Brownlee said emergency exit tunnels were built into the mine but that he didn't know if they could be accessed by the miners.

Whittall said the horizontal mine tunnel would make the rescue effort easier than if the shaft was at a steep angle.

"We're not a deep-shafted mine so men and rescue teams can get in and out quite effectively, and they'll be able to explore the mine quite quickly," he said. "They will work throughout the night and they'll work until they can go right throughout the mine and determine the extent of the incident and the safety of our employees."

Pike River has been operating since 2008, mining a seam with 58.5 million tons of coal, the largest-known deposit of hard coking coal in New Zealand, according to its website.

Pike River says its coal preparation plant at the site is the largest and most modern in New Zealand and processes up to 1.5 million tons of raw coal a year. It is country's largest single source of coal exports.

The mine's ventilation shaft was blocked by falling rocks in early 2009, delaying mining for months.

The mine is not far from the site of one of New Zealand's worst mining disasters _ an underground explosion in the state-owned Strongman Mine on Jan. 19, 1967, that killed 19 workers.

___

Associated Press reporter Tanalee Smith in Adelaide, Australia, contributed to this report.