With the UK's departure from the EU looming there are concerns a deal on the post-Brexit relationship may not be cobbled together in time for an orderly exit.
Britain and its European Union partners have failed to secure a breakthrough in Brexit talks largely because of seemingly intractable divisions over the best way to avoid a hard border on the island of Ireland.
They've spent two days in Salzburg, Austria trying to do just that, but with no clear solution in sight, the sides have tried to ramp up pressure on each other. Each side is urging the other to compromise while the EU issues constant warnings to Britain about the Brexit clock ticking.
French President Emmanuel Macron said on Thursday the Brexit plan proposed by British Prime Minister's Theresa May was unacceptable in its current form and that he expected new proposals from Britain in October.
"The Brexit teaches us something - and I completely respect British sovereignty when I say that - it showed that those who say that we can easily live without Europe, that everything is going to be alright, and that it's going to bring in a lot of money are liars," he said.
The French president, who has taken a hard stance on preserving the European Union's united front in talks on Britain's departure from the bloc, said Brexit showed other countries that leaving the EU had negative consequences.
Irish Prime Minister Leo Varadkar told reporters time is running short.
"We want avoid a 'No Deal Brexit,' but we are preparing for that. We are hiring extra staff and officials, bringing in IT system," he said.
"We are ready for that eventuality, should it occur."
Any Brexit deal will include a withdrawal agreement and transition period to smooth Britain's exit from the bloc.
Currently that's expected to last until the end of 2020 but if there is no deal to ensure no hard border in Ireland and a political declaration outlining future relations, then there will be no so-called transition period.
That could would lead to Britain crashing out of the EU on Brexit day, a development that in theory could see flights parked and trade between the two sides grind to a halt.
For Ireland, it's important not to undermine the hard-won peace after decades of sectarian tensions in neighbouring Northern Ireland.
"What we want to avoid is any new barriers to the movement of goods, any new barriers to trade, any new barriers to the movement of people," Varadkar said.
Dutch Prime Minister Mark Rutte labelled the Brexit negotiations "a balancing act" and the leaders will have further opportunities to thrash an agreement out when they meet again in Brussels on October 18 and again in mid-November.
Over dinner in Salzburg on Wednesday evening, May told the other leaders that Britain would not delay Brexit or hold a second referendum. She insisted that her proposals - the so-called Chequers plan - is the only option left.
Under Chequers, Britain would basically remain a member of the EU's single market for goods and abide by EU rules governing that market.
EU leaders say that is "cherry-picking" on the part of Britain, which would be able to go its own way in services and on other issues such as the freedom of movement of labour.