Michel Barnier, the European Union's (EU) chief negotiator, has warned that the ongoing negotiations on a post-Brexit trade deal with the UK were now at a "moment of truth" with only "a few hours" left for an agreement to enter into force by January 1, 2021.

"It's the moment of truth. We have very little time remaining, just a few hours to work through these negotiations," Xinhua news agency quoted Barnier as saying at the European Parliament in Brussels on Friday during the opening of a debate as MEPs met to vote on emergency measures in the event of a "no deal" Brexit.

"There is still a chance of getting an agreement, but the path to such an agreement is very narrow," he said, calling on everyone to assume their responsibilities.

He was speaking ahead of a last-ditch attempt to reach an agreement in talks with his British counterpart David Frost, despite the thorny remaining issues like fisheries.

"The unresolved issues in these few crucial hours that remain at our disposal are fundamental issues for the EU.

"We are not asking more nor less than a balance between rights, obligations and reciprocity. Access to market and access to waters are the other way round. No more, no less," Barnier said.

He claimed that, while British companies would retain their rights, EU fishing crews would lose out on guaranteed access.

"I don't think it would be fair, nor acceptable, if European fishermen were not allowed, following transitional rights, to have access to those waters."

Barnier said his team was striving for an agreement but "this is not an agreement that we are prepared to sign at any price".

Admitting he could not tell what may happen in the last hours of the negotiations, the chief negotiator called for preparations "for all eventualities".

Later, the European Parliament adopted contingency measures to ensure basic road and air connections in case no agreement is reached on EU-UK future relations.

The UK officially exited the EU on January 31 and will leave the bloc's single market and customs union at the end of this month, as the transition period will end on December 31.

Negotiators from Brussels and London are working round the clock to break the impasse, but no agreement has yet been found.

Also on Friday, British Prime Minister Boris Johnson said the two sides will continue the post-Brexit trade talks, but there remains "a gap that needs to be bridged".

"Obviously, the UK's position is always that we want to keep talking if there's any chance of a deal," he told Sky News.

"But we've also got to recognize that the UK's got to be able to control its own laws. It's what people voted for, and we've also got to be able to control our waters and fishing rights," he said.

The Prime Minister acknowledged that "things are looking difficult" and a no-deal Brexit "may be difficult at first".

But he reiterated that Britain would "prosper mightily" even under such a scenario.

"I think we've just got to get through this period and look to all the opportunities that will open up to this country in 2021," Johnson added.

Michel Barnier, the European Union's (EU) chief negotiator, has warned that the ongoing negotiations on a post-Brexit trade deal with the UK were now at a "moment of truth" with only "a few hours" left for an agreement to enter into force by January 1, 2021.

"It's the moment of truth. We have very little time remaining, just a few hours to work through these negotiations," Xinhua news agency quoted Barnier as saying at the European Parliament in Brussels on Friday during the opening of a debate as MEPs met to vote on emergency measures in the event of a "no deal" Brexit.

"There is still a chance of getting an agreement, but the path to such an agreement is very narrow," he said, calling on everyone to assume their responsibilities.

He was speaking ahead of a last-ditch attempt to reach an agreement in talks with his British counterpart David Frost, despite the thorny remaining issues like fisheries.

"The unresolved issues in these few crucial hours that remain at our disposal are fundamental issues for the EU.

"We are not asking more nor less than a balance between rights, obligations and reciprocity. Access to market and access to waters are the other way round. No more, no less," Barnier said.

He claimed that, while British companies would retain their rights, EU fishing crews would lose out on guaranteed access.

"I don't think it would be fair, nor acceptable, if European fishermen were not allowed, following transitional rights, to have access to those waters."

Barnier said his team was striving for an agreement but "this is not an agreement that we are prepared to sign at any price".

Admitting he could not tell what may happen in the last hours of the negotiations, the chief negotiator called for preparations "for all eventualities".

Later, the European Parliament adopted contingency measures to ensure basic road and air connections in case no agreement is reached on EU-UK future relations.

The UK officially exited the EU on January 31 and will leave the bloc's single market and customs union at the end of this month, as the transition period will end on December 31.

Negotiators from Brussels and London are working round the clock to break the impasse, but no agreement has yet been found.

Also on Friday, British Prime Minister Boris Johnson said the two sides will continue the post-Brexit trade talks, but there remains "a gap that needs to be bridged".

"Obviously, the UK's position is always that we want to keep talking if there's any chance of a deal," he told Sky News.

"But we've also got to recognize that the UK's got to be able to control its own laws. It's what people voted for, and we've also got to be able to control our waters and fishing rights," he said.

The Prime Minister acknowledged that "things are looking difficult" and a no-deal Brexit "may be difficult at first".

But he reiterated that Britain would "prosper mightily" even under such a scenario.

"I think we've just got to get through this period and look to all the opportunities that will open up to this country in 2021," Johnson added.