LATEST: A diesel spill caused by a high pressure tank on Lambton Quay closed part of the north end of the street and pavement this afternoon.
Senior Station Officer Nick Pyatt said diesel had leaked into the main switch room of Plunket House on Lambton Quay.
Workers isolated power to the eight-storey building and sealed the over-pressurised diesel tank.
Firefighters contained the diesel from entering drains, said Wellington Fire Service central communications shift manager Murray Dunbar.
"Fifty litres spilled there which will have to be absorbed."
A woman slipped and diesel splashed in her face after the spill erupted about 12.35pm outside a 2degrees store.
The north-bound road was closed between Balance and Bunny streets for about three hours.
The spill was caused when a tank underneath the street was overfilled by a tanker operator.
Mr Pyatt said a faulty gauge led to the error and the pressure in the tank needed to be reduced. High-pressure diesel was flammable and a potential danger to the public, Mr Pyatt said.
Hataitai man Anthony Xanthopol, 38, was standing nearby when the spill erupted from the ground.
"I heard a commotion. I looked over and the guy [operator] was trying to dampen down the diesel that was coming out. It was a fountain, but it didn't go high because he put his hand over it."
A middle-aged woman was walking past at the time and slipped.
"She fell on the pavement stones. As she fell she fell into the spray and got a bit on her clothes and in her eyes."
Mr Xanthopol came to her aid. She was later treated at the scene by a Wellington Free Ambulance paramedic and was not transferred to hospital.
"She's fine. They just wanted to make sure that her eyes were OK. I think she was a bit shaken at first. It's a foul smell."
- The Dominion Post
Is this the best summer ever?Related story: Wellington sizzles in January heat