Twenty-nine others are missing.
A company official had earlier said that five men had come out of the mine, but officials said they had seen no sign of the other three men.
Rescue teams rushed to the scene, but they're waiting for word that the mine is safe 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.
Investigators say shortly before the blast, the electricity went out in the mine, which may have caused ventilation problems, contributing to a buildup of gas.
Specialist teams were preparing for a rescue bid Saturday at the mine, located in rugged mountains near Atarau on New Zealand's South Island. But Tony Kokshoorn, mayor of nearby Greymouth who visited the mine, said it could be days before it was safe enough for them to enter.
"We are holding on to hope," he told reporters. "Look at Chile, all those miners were trapped and they all came out alive."
The Associated Press contributed to this story.