Dairy processing plants throughout the upper North Island are still scaling back or stopping operations as workers hurry to repair a leak to a major gas pipeline.
The leak in the Maui pipeline in the remote White Cliffs area north of New Plymouth is disrupting more than 2500 businesses, including power providers and steel mills.
Fonterra said its processing plants had been forced to throw out $20 million of milk a day while its operations were cut off by the leak.
In an update sent this afternoon, it said most of its plants in Waikato and Bay of Plenty would resume scaled back operations on limited gas supply within five to 16 hours.
However, its Maungaturoto, Kauri and Tip Top plants north of Auckland would remain closed, its statement said.
Trade and Operations director Gary Romano said processing capabilities would be limited to avoid putting strain on the smaller Vector gas pipeline.
"Given we are one of the 200 businesses receiving gas from this smaller line, we will need to restrict our use and scale back our processing capabilities to avoid gas supply being cut off again," he said.
At a press conference with acting Energy and Resources Minister this morning Vector chief executive Simon Mackenzie said the leakwill take more than two days to fix.
Workers have to carry out painstaking drilling work - focusing on 30cm at a time to avoid further damaging the pipe or the other gas pipeline that runs nearby.
Vector has promised hospitals and most dairy companies will have their gas supplies restored today, as it works to repair a leak in the Maui pipeline.
Hospitals, power stations, universities and other customers were last night urged to reduce their gas use.
But the full impact of the leak began to emerge this morning as problems spread to everything from burger chains to gyms.
Burger King was forced to close almost all its restaurants in the upper North Island and gymgoers at Les Mills had to endure cold showers.
A sign in the fast food chain's store on Auckland's Queen St this morning read:
"Due to the gas leak affecting New Zealand Burger King has been requested to close their restaurants until the issue has been resolved.
"We apologise for any inconvenience.''
Burger King spokeswoman Rachel Allison said the company was last night asked to close its stores by gas supplier Nova and didn't know how long the situation would last.
Staff had reported for duty and were carrying out maintenance work. Ms Allison said they were being "kept busy'' and being paid "at this stage''.
Les Mills clubs in Auckland City, Britomart, Hamilton, New Lynn and Takapuna were affected by the leak, said marketing director Guy Needham.
Members using the gym since 7am have had cold showers and the hot spa has also been affected.
Bread products under the Quality Bakers brand have also been affected by the leak, said Goodman Fielder director of corporate affairs Ian Greenshields.
The company produces and distributes a number of baking, bread, dairy, meat, and oil brands.
"We had to shut bakeries yesterday _ everything north of New Plymouth. There is a limited range (of Quality Bakers products), but we hope we will be able to maintain adequate supplies.''
The Meadowfresh milk brand would not be affected because the plant is in Palmerston North, said Mr Greenshields.
Auckland Council has begun shutting down gas supplies to its buildings and services, which could disrupt swimming pools and crematoria.
Mayor Len Brown urged residents to reduce use where possible.
Genesis public affairs manager Richard Gordon said large commercial customers had been asked to limit their gas use but domestic customers were not affected at this stage.
Mr Mackenzie said the leak was first reported by a farmer on Saturday, but Vector workers could not find a problem.
They were called back on Monday, when the leak was identified. The company then had to isolate gas on the Maui pipeline to find out where it was.
"It was reasonably evident given some basically bubbling to the surface of the gas. Once the gas pipe was isolated ... we then commenced excavation.''
He said civil aviation had been notified of the problem because the high-pressure gas rises into the atmosphere.
Fonterra farmers, reported to be throwing away up to $20 million of milk a day, are being asked to dispose of the milk in their paddocks not waterways.
Auckland's Middlemore Hospital has shut off heating in non-clinical areas, said Counties Manukau District Health Board spokeswoman Lauren Young.
She said the hospital was going "okay'' and assessing the situation day-by-day.
"We're trying to conserve our sterile supplies and our linen. We're asking staff to be careful.''
Hospitals run by the Waitemata board in Auckland's Waitakere and North Shore have switched from gas to diesel.
Spokesman Paul Patton said it was "business as usual'' and there had been no cancellations of surgery.
Auckland board staff have been asked to conserve linen and heating was being shut down where possible, said spokesman Mark Fenwick. Cooking would not be affected.
The laundry contractor to the Waikato board worked through the night to provide clean linen to their colleagues in Auckland, Waitemata and Counties Manukau.
Patients are being asked to use their own pyjamas, towels and facecloths due to the shortage of linen, said Waikato spokeswoman Mary Anne Gill.
Bread and milk, which were an important part of patients' diets, were being rationed, she said.
The Service and Food Workers Union says it has been deluged with calls from workers whose jobs are affected by the leak.
"Thousands of our members are employed in large food processing factories like Griffins and Bluebird in the upper North Island,'' said SFWU food industry leader Chas Muir.
Mr Muir said the SFWU was advising members that they should not be disadvantaged by the leak and should not lose any pay.
"We are advising members that any good employer will have insurance cover and the onus is on the employer to do the right thing.
"We are advising our members that if they are ready and willing to work it is the employer's responsibility to pay them.''