2000 Lotto tickets are being purchased every single minute ahead of tonight's record-breaking must-be-won Powerball draw.

Lotto outlets around the country are inundated with people buying tickets - there's $40 million up for grabs.

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Phone lines at Lotto outlets around the country are engaged as attendants try to get through queues of people.

Lotto NZ chief executive Wayne Pickup said they're selling five times as many tickets as they normally would on a Saturday.

He said they've never seen sales like this before.

"Since about midday, there have been well over 2000 tickets sold per minute," he said.

"The other thing is that the busiest time for us in any week is after three o'clock on a Saturday. We're not sure how big it's going to get, all we're doing at the moment is trying to get up with demand."

Mr Pickup said while the system has no limit on how many tickets to sell, things could get a bit clunky.

"There's no limit, there's probably a capacity limit at some stage, so we're urging people to avoid queues, the website might be a bit slow around seven o'clock tonight, so if you want a ticket, don't wait."