A Northland geothermal power station has been declared safe after explosive pentane gas leaked from the plant.
Emergency services were called to the Ngawha plant near Kaikohe at about 5.45am on Thursday. Nine fire engines were sent to the plant.
Power company Top Energy said there was no explosion when a relatively small amount of pentane leaked.
Communications manager Peter Heath said the company was looking into how much gas actually escaped. He told Radio New Zealand's Morning Report a safety valve was released, though it is not clear why, and as part of the safety process the gas was released.
He said the sole operator on the site called the fire service and plant was shut down. "There were earlier reports this morning that there was a fire and an explosion but that is not the case," he said.
Pentane gas is used create electricity at the plant, he said, and is very light with a low flashpoint. "It's basically lighter fluid."
The gas, which powers the turbines, was released with a loud bang, waking residents of Ngawha village, several kilometres away. By 7.30 am the site was declared safe and most of the plant was running as usual.
The Fire Service said it appeared all safety operations worked properly and its crews had been stood down.
Mr Heath said the gas posed a threat to staff, which is why the site had been evacuated, but it was not likely to have been dangerous to people in the wider area.
Top Energy chief executive Russell Shaw said gas is normally released through a dump valve if, as is not uncommon, one of the generators trips.
But he said in this case the dump valve did not work and the gas was released through the back-up safety valve, which makes a very loud noise. The company is investigating why the dump valve did not work.
The station produces about 70 percent of all electricity consumed in the Far North, Top Energy's website says. It was first commissioned in 1998 and a decade later the company completed a $77 million expansion of the original plant.