A post-Brexit trade deal can be struck within days, Ireland's foreign minister Simon Coveney said as he urged European Union members to "hold our nerve".
UK and EU negotiators, led by Lord Frost and Michel Barnier, talked late into the night on Wednesday, fortified by a delivery of pizzas, as efforts continued to thrash out a deal which needs to be in place by the end of the month.
Mr Coveney said there is still a "good chance" a deal can be done.
"It's the time to hold our nerve, to trust Michel Barnier, who has done a phenomenal job to date," he said.
"I believe, if we do that, there's a good chance that we can get a deal across the line in the next few days."
Downing Street sources played down the prospect of an imminent breakthrough.
"I haven't seen any white smoke," one insider told the PA news agency.
Businesses are frustrated with the uncertainty around trading arrangements once the UK leaves the single market and customs union at the end of the year.
Tesco chief executive Ken Murphy told Sky the supermarket giant is preparing for a no-deal scenario.
"We have been doing everything in our power to make sure that we are well placed to continue trading, to continue to supply our customers regardless of whether there is or isn't a no-deal Brexit," he said.
"The biggest challenge we face really is the movement of product between borders, the movement of product between Great Britain and Northern Ireland and, of course, between mainland Europe and the UK.
"That's the one area where we really would urge the Government to give us some clarity and to allow us to prepare event better for the end of December."
On Wednesday, Boris Johnson used the language of the referendum campaign to spell out to Brussels that the UK's "bottom line" on a post-Brexit trade deal is to "take back control".
The Prime Minister said he is "absolutely committed" to trying to secure a deal "if we can" amid warnings that talks with the EU have reached a "make or break" point.
Reports have suggested that the UK has watered down its demands for control of fishing rights, by asking EU fishing fleets to hand over up to 60% of the value of stocks currently caught rather than the 80% previously sought.
But this falls short of EU demands in one of the most symbolically important aspects of the negotiations.