The European Union's chief Brexit negotiator Michel Barnier on Thursday repeated a call for a decision from London on its withdrawal deal, rather than seeking a delay.

"Today, we need above all a decision, it's more important than extra time," Barnier told a news conference in Vienna. European leaders have already warned that any postponement would come with conditions.

"The duration of any extension would be linked to the question of what to do with the time," Barnier said.

"If it's to sort out a technical question, it could be a few weeks to go up to the eve of the European elections."

Barnier also raised the possibility of a longer extension in the case of "new British choices" but pointed out that "if at the time of the European elections the British are members of the Union, legally speaking they like other countries would have the obligation to organise elections".

Barnier was speaking after talks with Austrian Chancellor Sebastian Kurz, who also saw a  problem with the European elections.

"The participation of a country that wishes to leave the European Union in European elections would be more than absurd," Kurz said.

"So our goal has to be that the exit, if it has to happen, happens in an orderly fashion," he added.