(Reuters) - Dreams of vast riches from a record Powerball jackpot of at least half-a-billion dollars drove enthusiastic ticket-buying across the United States ahead of the Wednesday night draw, and continued heavy sales could nudge the payout higher, authorities said.

Powerball has not had a winner for two months, and the pot has already grown by nearly $175 million due to brisk ticket sales after no one won the top prize in Saturday's drawing.

The next draw for the prize on Wednesday night would dish out a whopping $327.4 million and counting if paid as a lump sum. Alternatively, the $500 million can be paid out in an annuity over three decades.

"It's been crazy," said Chris Lewis, manager of a 7-Eleven convenience store in Westminster, Colorado, that sold 2,000 tickets in 11 hours on Tuesday. "I'm worn out because it's been so busy today. Amazing."

Powerball is sold in 42 states, Washington, D.C., and the U.S. Virgin Islands. There have been nearly 300 jackpot winners over the past 20 years, taking home payouts of over $11.6 billion.

Among dreamers lining up at an Arizona grocery store in Tucson for a shot at Wednesday's prize was metal shop worker Errol Simmons, 54, entrusted with a list of lucky numbers by a dozen or so co-workers.

"I've got to get this right," he said as he checked through the list. "I don't want to be the guy who lost us half a billion dollars because I couldn't count.

"If we win, I'll buy a new truck," he said. "For each day of the week."

Looking sharp in a blue pin striped suit, Portland, Oregon, financial adviser Aaron Pearson, 36, said he was taking care to pick his own numbers for the first time - although he was unsure what he would do with the huge jackpot should he win.

"I have no idea. I'd invest it and live off of it. I'd give to charities. I'd start a foundation," he mused.

The chance of winning the jackpot are about one in 175 million, compared to about one in 280,000 for being struck by lightning.

Despite the long odds, the record payout has drawn interest from around the world, said Mary Neubauer, a spokeswoman for the Iowa Lottery, where Powerball is based. Lottery officials have received calls and emails from people outside the United States asking if they can buy a ticket from afar. They cannot.

"Sales across the country are just through the roof. It means lots of people are having fun with this, but it makes it difficult to keep up with the (jackpot) estimate."

The previous top Powerball prize of $365 million was won in 2006 by ConAgra slaughterhouse workers in Nebraska.

In March, three winning tickets shared the largest U.S. lottery jackpot, the $656 million Mega Millions drawing.