Farmers are throwing away $20 million of milk a day because of a leak which has closed a Maui gas pipeline.
All industrial gas-users in the upper North Island, including hospitals, power stations and universities, have been urged to stop using the fuel.
Fonterra has shut all but two of its plants north of Taupo because they cannot process milk without gas.
Hospitals in Waikato are asking patients to bring in their own pyjamas and towels as the linen-cleaning company for all hospitals from the central North Islands upwards moves its operations to Hamilton.
The pipeline, which links the Maui gas field to the upper North Island, was closed yesterday morning after a serious leak was found in the remote White Cliffs area, north of New Plymouth.
Vector, which manages the pipeline, said it was working to fix the problem but it did not know how long it would take to restore gas.
Spokeswoman Sandy Hodge said a team of geothermal scientists was at the site trying to establish where the leak occurred. Engineers were working out solutions.
"So what we're doing is working off several models and scenarios so as soon as we know what we're dealing with we have the solution and can fix it quickly," Mrs Hodge said.
Household customers had not been asked to limit their gas use.
Genesis Energy has switched its Huntly power station from gas to coal.
A Fonterra spokesman said the effect of the closure on the company and its farmers, who are being asked to throw out all their milk, had been "huge".
About 30 million litres would be lost each day the closure continued, at a cost of of $20 million a day, "so there is a big impact for us".
Fonterra is able to process only five million litres a day at its Waitoa and Te Awamutu plants, which are able to run on coal.
Auckland hotels have also restricted their gas use, and if the pipeline is not repaired quickly, guests may have to take cold showers.
A spokesman for Accor, which owns nine hotels in Auckland, said it had enough gas to keep it going for the next few days.
It would evaluate the situation when more information was available from Vector.
Auckland University has stopped all gas use in buildings other than for accommodation.
The leak couldn't come at a worse time for Fonterra farmers, who are at the height of a record "spring flush", as the new milking season is known in the industry. APN