Video | Blast fears delay search for 29 New Zealand miners

According to latest reports, it was yet known if the 16 employees and 13 contract miners survived the initial powerful explosion on Friday.

Repeated attempts to contact them have been fruitless, Pike River Mine Ltd's chief executive Peter Whittall said. "We haven't heard a thing.” Attempts to reach the miners through a working phone line connected to the bottom of the mine remained unanswered.

So far, only two dazed and slightly injured miners have made it out of the mine. They stumbled onto the surface only hours after the initial blast shook the mine and passed through its 354-foot (or 108-metre) long ventilation shaft.

Whittal has been reported as saying that the blast was most likely caused by coal gas lighting. So far, the extend of the damage suffered by the mine is unkown.

The police search controller, superintendent Gary Knowles, said rescuers were ready to go as soon as air quality tests showed low enough gas levels for a safe search.

"We're not going to put 16 men underground and risk their lives," he told reporters.

He remained confident that the missing miners were alive.

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

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.

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.