The "shock" of Brexit has brought the rest of the bloc closer together, incoming European Commission chief Ursula von der Leyen said Friday.

The turbulent Brexit process has reminded many "who have their doubts about the EU" of the benefits of being in the club, she said in Berlin.

In a wide-ranging speech on the eve of the 30th anniversary of the fall of the Berlin Wall, the former German defence minister said the bloc had shown it could grow stronger in times of crisis.

"As paradoxical as it sounds, the shock of Brexit has strengthened our unity," she said.

"Because it has not only shown what it means to leave the EU, but also how much each country stands to gain as part of the European Union."

Defying predictions that Britain's decision to leave would spark discord in the bloc, von der Leyen said "as different as we are, when it comes to the Brexit negotiations the 27 members stand together".

Britons voted in 2016 to leave the European Union, sending shockwaves through the continent.

But a crippling political deadlock at home has seen Britain's departure date delayed three times, and the country is now gearing up for a snap election next month that could trigger fresh Brexit uncertainty.

How to avoid a hard border between the Republic of Ireland and Northern Ireland has been one of the key stumbling blocks in the tortuous process.

The remaining EU members have firmly backed Dublin's position that there could be no barriers on the island that would jeopardise the 1998 Good Friday Agreement that ended three decades of sectarian violence.