The largest lottery jackpot in history, $640 million (£400 million), has been won by a ticket holder in Maryland, and officials were waiting early on Saturday to see if there are other winning tickets.
Maryland lottery officials announced that a winning ticket was purchased at a store in Baltimore County, though they had not identified the winner yet.
Some 625 million tickets were expected to have been sold, more than two for every American resident.
The odds of winning – at 176 million-to-one
Long queues snaked out of corner stores as buyers lined up to try their chances.
A single winner could claim yearly payments or a one-time cash option of $462 million, Mega Millions spokeswoman Kelly Cripe said.
The previous largest Mega Millions jackpot was $390 million in 2007, and was split between two ticket holders in Georgia and New Jersey.
About half of the lottery money is paid out to ticket holders in the form of winnings, 35 percent to state governments and 15 percent to retailer commissions and lottery operating expenses.