She pledged to continue with her plans for the looming Brexit talks, but newspapers said her standing had been diminished.
The Sun, Britain's biggest-selling newspaper, simply said "Mayhem" on its front page.
"She gambled... and she lost," the Conservative-backing tabloid said.
"Britain is about to find out the price of that failure. Brussels will be licking its lips.
"At the start of the election campaign, she was seen as a safe pair of hands.
"It is almost inconceivable that seven weeks later, the Tory majority has been wiped out."
"Britain on a knife edge," headlined the pro-May Daily Mail, saying her gamble in calling a snap general election to boost her majority had "backfired disastrously".
The London Evening Standard is edited by George Osborne, sacked by May as Britain's finance minister when she took office in 2016.
"Queen of Denial", said its front page after she returned to Downing Street to form a government without mentioning her losses.
"PM ignores disaster at polls as she pledges to provide 'certainty'."
Its cartoon inside showed May in the pocket of a hardcore Ulster unionist in traditional Orangeman.
"Her authority is non-existent," the editorial said.
"We now have a minority Conservative government that is in office but not in power."
"Shock for May", said The Daily Telegraph, a conservative broadsheet.
"May's big gamble fails," said The Times.
"A failed campaign leaves Theresa May humbled and her party reeling," its editorial said.
"It is hard to see her authority going unchallenged by cabinet colleagues for long."
The Financial Times business daily said May "seeks to cling to power with N. Ireland party", referring to the Democratic Unionists, on whose support she will now rely.
The pro-Labour Daily Mirror said May's authority was "hanging by a thread" following "the most sensational political disaster for generations".
In the outgoing parliament, May had a slim working majority of 17 seats in the 650-seat House of Commons.
With one result to come Friday, the Conservatives had 318 seats, Labour 261, the Scottish National Party 35 and the Liberal Democrats 14. The Democratic Unionists won 10 seats.
At the start of the election campaign, opinion polls predicted May would possibly romp home with as high as a triple-digit majority.