Former chancellor George Osborne, axed under Theresa May, said the exit poll indicated a "catastrophic" night for the Conservatives.
He told ITV: "It is early days, it's a poll, if the poll is anything like accurate this is completely catastrophic for the Conservatives and for Theresa May
"It's difficult to see, if these numbers are right, how they would put together the coalition to remain in office."
Tory Defence Secretary Sir Michael Fallon told the BBC: "This is a projection, it's not a result.
"These exit polls have been wrong in the past."
Shadow foreign secretary Emily Thornberry said it was still early but told Sky News: "They have been right for the last 20 years or so, 30 years, so I think we're on the verge of a great result.
"Just think only seven weeks ago the hubris of the Prime Minister who was 20 points ahead, who wanted to have a blank cheque, she wanted to do whatever she wanted with the country with Brexit, with the economy, with our National Health Service and we said no and we meant it."
Ukip leader Paul Nuttall wrote on Twitter: "If the exit poll is true then Theresa May has put Brexit in jeopardy. I said at the start this election was wrong. Hubris."
Former England striker and Match Of The Day presenter Gary Lineker, referring to Mrs May's decision to call a snap election, wrote on Twitter: "I think Theresa May has won own goal of the season."
It was a theme picked up by Christopher Snowdon, the Spectator writer. Referring to an interview Mrs May gave earlier in the week, he wrote on Twitter: "This is a new contender for the naughtiest thing Theresa May has ever done."
Former Great British Bake Off host Sue Perkins offered her own take on the future of Ukip leader Paul Nuttall, who has previously been questioned about some of his claims about his personal life.
She wrote on Twitter: "Ukip is finished. But at least Paul Nuttall can go back to his day job as Poet Laureate."