Hot weather has sent beer consumption skyrocketing - causing havoc for brewing giant Lion, which is struggling to keep up with demand.

The company has fallen behind on deliveries across the North Island and sales are up 20 per cent on last year, Lion spokeswoman Genevieve O'Halloran said.

The supply issue was widespread, she said, effecting deliveries for soft drink also.

"Summer arrived with a bang - it's like a light switch has been flicked, and that's the key reason demand has shot up," she said.

"The market is growing one per cent over the year and in the last couple of weeks we've seen demand spike 20 per cent compared to the same period last year, and the orders coming through to our warehouses are up 40 per cent."

Lion's Emerson beer sales are up 140 per cent compared to last year and Panhead brews up 60 per cent and Corona sales up 50 per cent, O'Halloran said.

It had increased staff working on logistics, extended delivery hours and staff were working late nights, weekends to rectify the problem, she said.

"We set high standards for ourselves and we are really upset and disappointed to be letting our customers down.

"We are doing everything we can to make sure that we manage this issue."

O'Halloran said Lion was making good progress on the issue.

Although the company had planned for the summer trading period, O'Halloran said it hadn't anticipated such strong demand.

"We always plan for a spike in demand going into Christmas, going into summer, but it doesn't usually arrive with such a bang," she said. "It's an unprecedented run of really good weather, which has really driven up demand."

Emma McCashin, president of Brewers Guild of New Zealand, said the organisation had seen "really strong" beer sales in recent weeks.

"No doubt this has been helped by the wonderful weather we have been having," McCashin said. "But anecdotal feedback from retailers is that more Kiwis are [now] drinking beer as their beverage of choice."

The Brewers Association of New Zealand said an unprecedented run of hot weather had created unusually high demand compared to the same period in previous years.