Garry and Ursula Scanlon were struggling to carry their armfuls of seafood at Newcastle Fishermen's Co-op on Friday.
"We've just come down from Cessnock. My wife's got a handful; I've got a handful. We're out of here," Garry said as he lined up at the cash registers.
The couple bought oysters, prawns and leatherjackets for the weekend and Christmas day.
"It's never been this busy when we've been before," Ursula said as shoppers lined up out the door to get into the Wickham store.
Co-op chief executive Rob Gauta said he, too, was surprised by how many people had turned up three days out from the big day.
"We've learnt not to expect. Every year Christmas falls on a different day, and it's different every year," he said.
"Christmas eve will be the busiest day. Sometimes the day before that is even the same or busier.
"We haven't had it on a Monday for a long time, so what's today going to bring? We'll see."
The co-op opens at 7am on Christmas eve.
Mr Gauta said in previous years some customers had camped overnight to secure spots at the front of the line-up.
"I'd probably call them crazy," he said.
He said the co-op should have enough oysters and prawns to serve most customers on Sunday, though he recommended arriving before noon.
"Prawns should be fine. It's touch and go what time we'll get them in the morning.
"They'll arrive in Sydney at 2am and hopefully we'll have them in time. It's been a bit of a problem with the rain in northern Queensland and roads being blocked off.
"Everything else we're confident we'll be fine.
"In previous years, if you're going to be after midday on Sunday, expect that we might run out of a few things.
"If we're going to run out, it will be after 11am or midday on Sunday."
He said prawns and Port Stephens oysters were the most popular seafood at Christmas, and salmon had been popular this year.
"We'll probably do about 4000 dozen oysters over the next three days and six tonnes of prawns.
"We've got wild-caught prawns from South Australia which are frozen and we defrost and fresh farm prawns from Queensland."
Mr Gauta described the pre-Christmas rush as "organised chaos".
"It's three months in the making. We're getting deliveries nearly every day of different products: oysters and prawns, in particular.
"Our biggest positive is our biggest liability: we're selling fresh seafood. Getting it here and getting it fresh is difficult, but we do it every year."
The co-op stopped taking online orders, each requiring a minimum spend of $350, on Wednesday night.
"I think we've got over 300 orders. They're all large orders, over $350," Mr Gauta said.
"That's a logistical nightmare on its own, but customers want that and that's fine."
He said some customers had complained about the $350 minimum but allowing small online pre-orders would be logistically impossible.
"We can serve you faster in the shop than we can pack an order," he said.
