The European Union warned Britain Friday that delaying Brexit negotiations after Prime Minister Theresa May failed to win a majority in elections could wreck the chance of securing a divorce deal.

Brussels had set June 19 as the start date for talks, but the bloc's leaders said that was now in doubt after Prime Minister Theresa May's gamble to strengthen her parliamentary mandate backfired.

EU President Donald Tusk bluntly warned that the clock was now ticking for negotiations on Britain's exit and a new trade deal before it formally leaves the bloc in March 2019.

“We don't know when Brexit talks start. We know when they must end. Do your best to avoid a 'no deal' as result of 'no negotiations',” former Polish prime minister Tusk wrote on Twitter.

European Commission chief Jean-Claude Juncker said the bloc had been ready “for months” to negotiate but suggested talks could be held up while Britain figures out its new top team.

“The dust in the UK now has to settle,” Juncker was quoted as telling Sueddeutsche Zeitung newspaper. EU Brexit negotiator Michel Barnier indicated the remaining 27 members were prepared to be flexible.

“Brexit negotiations should start when UK is ready; timetable and EU positions are clear. Let's put our minds together on striking a deal,” the Frenchman said on Twitter.

Barnier had previously set a timetable of talks starting in the week beginning June 19, with agreement on initial issues by autumn of this year and a provisional Brexit deal in October 2018.

But EU budget commissioner Guenther Oettinger said Britain's May was now likely to be a “weak” partner.

“The British need to negotiate their exit but with a weak negotiating partner, there is a danger that the talks are bad for both parties,” Oettinger told German radio, adding that “the next few hours or days will indicate if the other negotiating party can even begin talks because without a government, there can be no negotiations.”

'Clock is ticking'

Manfred Weber, the head of the European Parliament's largest group and a key ally of German Chancellor Angela Merkel, said May had caused “chaos”.

“EU is united, UK is deeply split. PM May wanted stability but brought chaos to her country instead,” tweeted Weber, who leads the centre-right European People's Party.

“The clock is ticking for Brexit. Therefore the UK needs a government soon. The date for the beginning of negotiations is now unclear.”

European Parliament Brexit pointman Guy Verhofstadt compared the British outcome to former British prime minister David Cameron's ill-fated decision to call last year's Brexit referendum.

“Yet another own goal, after Cameron now May will make already complex negotiations even more complicated,” Belgian ex-prime minister Verhofstadt said on Twitter.

Gianni Pittella, leader of the socialist bloc in parliament, added: “It's a disaster for May. Her huge gamble has backfired spectacularly. She has no credibility in UK or Europe. She should resign.”

When the talks do begin, experts say there could be a very different approach from the “hard Brexit” advocated by May that would involve leaving Europe's single market and curbing European immigration.

“What the UK asks for might not be quite as hard, quite as tough as she was asking for before. We might see a softening of the stance in response to this election result,” said Simon Hix, politics professor at the London School of Economics.

His LSE colleague Paul Kelly said the result would weaken May's hand in Brussels, where she is due to attend a summit on June 22 and 23.

“Merkel will notice that, (French President Emmanuel) Macron will notice that. Everybody will notice that and that changes the dynamic,” Kelly said.