The UK and EU continue to negotiate as talks on a post-Brexit trade deal enter another critical 48-hour period.
Talks in Brussels are understood to be focused on how many years it will take to phase in new fisheries arrangements.
With the two sides at odds over access to UK fishing waters and quota levels, the EU's negotiator said the "moment of truth" had arrived and there were "only a few hours left" to seal an agreement.
Boris Johnson has vowed to keep talking but warned gaps had yet to be bridged.
Senior MEPs in the European Parliament have said they will not be "rushed" into signing off a deal on their side and want to see the text of any agreement by Sunday if they are to approve it by the end of the year.
The UK will stop following the EU's trading rules in less than two weeks time.
If there is no agreement by 1 January, the two sides will rely on World Trade Organization (WTO) rules to govern exports and imports, which could see charges introduced on goods being sold and bought - and could lead to an increase in prices.
Speaking in the European Parliament on Friday, the EU's chief negotiator Michel Barnier said it was "the moment of truth" for the talks and while there was still a "chance" of a deal, the "path was very narrow".
Earlier, he met fishing ministers from EU states to discuss the continuing divisions over the issue.
The two sides have been at odds over the length of time it will take to introduce new arrangements once the UK leaves the bloc's Common Fisheries Policy.
The UK, led by its chief negotiator David Frost, has insisted its sovereign rights over its waters must be respected from day one and its fleets must be able to keep a much larger share of their own catch.
The EU is insisting on a much longer transition period, with guarantees on access and how catches are distributed.
Mr Barnier warned on Friday that if the UK wanted to reduce access for EU fishing vessels then it would "maintain its sovereign right" to impose new conditions on UK firms' access to its common market for goods.
In response, Mr Johnson said the UK side was willing to keep talking but things were looking difficult and urged the EU to "come to the table" with new proposals that recognised the UK's autonomy.
The two sides are reported to have made progress in recent days on the issues of fair competition and what to do if the UK is deemed to get an unfair competitive advantage by moving away from EU rules and standards.
If a deal is reached between the two sides, it would need to be agreed by parliaments in the UK and the European Union's member states.
UK MPs have now finished for the Christmas break, but Cabinet Office minister Michael Gove said on Thursday that they could be called back to ratify a deal in the coming days, were one to be agreed.
- Brexit happened but rules didn't change at once: The UK left the European Union on 31 January 2020, but leaders needed time to negotiate a deal for life afterwards - they got 11 months.
- Talks are happening: The UK and the EU have until 31 December 2020 to agree a trade deal as well as other things, such as fishing rights.
- If there is no deal: Border checks and taxes will be introduced for goods travelling between the UK and the EU. But deal or no deal, we will still see changes.
Credit: The BBC