Legions of players have been undeterred by one-in-292m odds of scooping Wednesday night's Powerball draw.
The winner can choose to be paid the full jackpot in annual instalments for 29 years or take $930m as a one-off payment, before taxes.
Lottery officials say people have been flocking over the border from Mexico and Canada to buy tickets, as players do not have to be US citizens.
Hundreds of people have been queuing at some outlets for a chance to play the game.
The Multi-State Lottery Association says if there are no winners, the jackpot will roll over to $2bn on Saturday with a lump sum payout of $1.24bn.
Some 85.8% of possible number combinations have been picked for Wednesday evening's draw, lottery officials say.
The jackpot for the twice-weekly game has soared from $40m on 4 November.
A ticket holder must match all numbers on six balls - five white ones from a drum containing 69 balls, and a red one pulled from a drum with 26 - to hit the jackpot.
"Sales are doing exponentially more than we've ever done before," Gary Grief, chair of the Powerball game group, told AFP on Tuesday.
Workers at a restaurant in New Jersey last week celebrated winning the Powerball lottery without realising they had matched numbers for the wrong day.
The previous US jackpot record of $656m, on March 30, 2012, was scooped up by three winners from North Carolina, Puerto Rico and Texas.
The world's richest lottery is Spain's annual Christmas El Gordo, which in 2015 handed out 2.2bn euros ($2.4bn), but capped individual wins at 400,000 euros.