Two dazed and slightly injured miners stumbled to the surface hours after the blast shot up the 354-foot- (108-meter-) long ventilation shaft at the Pike River mine. Video from the scene showed blackened 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.
A company official had earlier said that five men had come out of the mine, based on information provided by the two men who had surfaced. By Saturday morning, however, officials had seen no sign of the other three men.
By daybreak, no communication had been received from any of the missing workers, the company said, and rescuers were unable to enter the mine because of the risk of a buildup of explosive methane gas.
"There could be another explosion," said mine safety expert David Feickert, who noted that officials don't what caused the original ignition, and rescuers will enter the mine only when it is safe.
Peter Whittall, Pike River Coal Ltd.'s chief executive, said officials would have enough analysis in six to eight hours to decide whether a rescue team can go underground, adding that the missing miners would have to deal with such hazards as air pollution, high levels of methane and carbon dioxide, and low levels of oxygen.
Each miner carried 30 minutes of oxygen, enough to reach oxygen stores in the mine that would allow them to survive for "several days," said Pike River chairman John Dow.
"This is a search and rescue operation, and we are going to bring these guys home," police superintendent Gary Knowles told reporters.
Unlike the accident in Chile, where 33 men were rescued from a gold and copper mine last month after being trapped a half-mile (one kilometer) underground for 69 days, officials did not have to worry about the presence of methane gas, Feickert said.
He added, however, that the Pike River mine has two exits, while the mine in Chile had only one access shaft that was blocked.
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 Friday's explosion and that failure may have caused ventilation problems and contributed to a buildup of gas. The power outage continued to frustrate efforts Saturday 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."
Kokshoorn was hopeful the missing workers could survive like the Chilean miners, whose rescue - played out on live television - captivated the world.
"We are holding on to hope," Kokshoorn said. "Look at Chile, all those miners were trapped and they all came out alive."
Whittall had said Friday that 27 were missing, but on Saturday he told a news conference the number was 29 - 16 miners employed by the company and 13 contractors.
The coal seam at the mine is reached through a 1.4-mile (2.3-kilometer) horizontal tunnel into the mountain. The seam 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.
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 the workers underground were together.
Deputy Mayor Doug Truman said the blast was so powerful that one of the workers who came out of the mine described being only a mile (1,500 meters) inside the shaft when he was blown off his machine.
"The mine vents have ... scorch marks - so it must have been a reasonably big explosion," Truman told New Zealand's National Radio.
Energy Minister Gerry Brownlee said the explosion occurred 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 a half-hour later. That contact was with one of the two men who came out.
The two men who surfaced were taken to a hospital for treatment of minor injuries and were being interviewed to determine what happened, 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 tunnel would make any rescue 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.
While Pike River Coal is a New Zealand-registered company, its majority owners are Australian. There are also Indian shareholders.
New Zealand Prime Minister John Key said the government has told the company it will provide any support that is required. He also said the Australian government has also contacted the New Zealand government to offering its support and assistance.
Pike River has operated 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.
It said 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 work 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.
New Zealand has a generally safe mining sector, with 181 people killed in 114 years. The worst disaster was in March 1896, when 65 died in a gas explosion. Friday's explosion occurred in the same coal seam.
Associated Press writer Tanalee Smith in Adelaide, Australia, contributed to this report.