Rescue On Hold For 29 Trapped In New Zealand Coal Mine

(CNN) The fate of 29 New Zealand coal miners and contractors remains a mystery more than 20 hours since they were last above ground, with rescuers awaiting word that conditions are safe to go after the trapped men.

An explosion rocked the Pike River mine, on New Zealand's west coast between Greymouth and Reefton, around 4 p.m. Friday New Zealand time. Two men walked out with minor injuries, but their colleagues -- ages 17 to 62 -- were trapped as much as 2.2 kilometers (1.4 miles) from the tunnel's opening and have not been heard from since.

For now, authorities are monitoring results from a series of tests to determine if the air-quality underground is safe enough to send in help. The four tests conducted thus far, focusing on carbon monoxide levels, have been "inconclusive," said Pike River Coal CEO Peter Whittall at a Saturday afternoon press conference.

The rescuers are miners themselves, according to Gary Knowles, superintendent of the Tasman Police District, who is heading the rescue effort. For now, they are conducting drills and ready to go in at a moment's notice.