Two people have been badly injured in an explosion at a South Auckland house.
Emergency services were called to a two-story block of units on Clayton Ave, Otara, about 2.50am.
A woman living nearby, Gail Katene, said she was woken by a big bang.
"[I heard] one big bang and I came running out and I heard that there was a gas explosion.
"You could hear everyone screaming in the building coming out of it because they were saying 'it's ready to blow up, it's going to blow up'," she said.
Ms Katene said the people who live in the flat that exploded are teenagers.
"I spotted one of the guys jumping from the balcony, the second floor.
"All I could hear was this guy groaning saying 'get help, get help'," she said.
Fire Service northern shift manager Scott Osmond said it appeared they had been huffing - involving inhaling gas from a canister - when one lit a cigarette.
Police said one person suffered critical injuries while the other was in a serious condition.
The Fire Service said both were in a critical condition.
Both have been taken to Middlemore Hospital.
Fire investigators and police are working to establish what caused the blaze.