Boris Johnson and the EU have both warned they are unlikely to reach a post-Brexit trade deal by Sunday.
European Commission President Ursula von der Leyen said no deal was the most probable end to “difficult” talks.
And the UK prime minister argued the EU needed to make a “big change” over the main sticking points on fishing rights and business competition rules.
The Sunday deadline was set by the two leaders after months of talks failed to achieve an agreement.
If a trade deal is not reached and ratified by both sides by 31 December, the UK and EU could impose taxes – tariffs – on each other’s goods.
This could lead to higher prices, among other changes.
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As talks between officials continue, the EU is determined to prevent the UK from gaining what it sees as an unfair advantage of having tariff-free access to its markets, while setting its own standards on products, employment rights and business subsidies.
It is also warning that, without access to UK waters for EU fleets, UK fishermen will no longer get special access to EU markets to sell their goods
But the UK argues that what goes on in its own waters, and its wider business rules, should be under its control as a sovereign country.
The two sides also disagree on whether the European Court of Justice should settle future UK-EU trade disputes.
The EU has rejected Mr Johnson’s request to bypass the European Commission and speak directly to French President Emmanuel Macron and Germany’s Angela Merkel about the unresolved issues.
According to EU officials, he was told discussions could only take place through the bloc’s chief negotiator, Michel Barnier.
Speaking on a visit to a vehicle battery factory in Blyth, Northumberland, Mr Johnson said: “We’re always hopeful and… our team is still out there in Brussels.
“If there’s a big offer, a big change in what they’re saying, then I must say that I’m yet to see it.”
If there was no deal, the situation would still be “wonderful for the UK”, as the country could “do exactly what we want from 1 January”, he added, even if this was “different from what we set out to achieve”.