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Dunedin's Speight's Brewery has nearly doubled production because of the Canterbury quake.
Speight's Dunedin manager John Craig said production had increased from 1600 kegs a week to 3000.
The brewery's 11 employees had been working extra hours since Monday and would operate the brewery six days a week, rather than four.
Millions of dollars of stock was destroyed at Lion Nathan's Canterbury Brewery in St Asaph St. The brewery is also out of action until Monday, at the earliest.
As well as regular Speight's, the Dunedin brewery had stepped up production of specialty beers, such as Old Dark and Summit. In the case of Summit, the brewery was supplying the whole country, rather than just the South Island, Mr Craig said.
The extra production would continue for two weeks at least.
Lion Nathan spokesman Neil Hinton said millions of dollars of stock in the Christchurch warehouse was destroyed in Saturday's quake.
Buildings had had sustained minor damage, but had now been cleared for use.
However, the brewery could not discharge into the city's fragile sewer system the large amounts of wastewater it produced. It was hoped production could resume on Monday.
Both Auckland and Dunedin had stepped up to meet demand.
"The boys in Dunedin are cranking it out," Mr Hinton said.
Foodstuffs' South Dunedin distribution centre was running 24 hours, seven days a week, to cope with the extra demand caused by the quake, South Island chief executive Steve Anderson said.
Food shortages in the company's stores - New World, Pak'n Save, and Four Square - would be less severe for Dunedin and the South because of Dunedin's distribution centre, he said.
All three Foodstuffs Christchurch distribution centres had been damaged, with one unable to be used until extensive repairs had been carried out.
Christchurch staff were "spooked" by the aftershocks and some were unable to work because of the stress, he said.
In Christchurch, there had been shortages of bread and water, because of higher than usual demand.
With boil notices for water, and fewer cafes open to make workers' sandwiches, demand for the basics was higher.
The situation had eased with the boil-water notice lifting, Mr Anderson said.
Customers were warned to expect shortages of luxury products throughout the South Island, and some budget "home brand" product lines had been affected.
Progressive Enterprises, which includes Countdown and Super Value, has also warned customers of possible disruption to food supplies.