Fighting climate change, safeguarding the rule of law and finding a modern model for growth must be at the heart of the European Union, leaders including Taoiseach Leo Varadkar have agreed at talks aimed at showing unity despite the damage from Brexit.

However, their informal gathering in Romania did not produce clear decisions on how to achieve the ambitious goals.

The leaders of all members except the UK met on Europe Day in the city of Sibiu.

Ahead of European Parliament elections later this month, the 27 leaders also had a first look at assigning the bloc's most powerful jobs later this year.

"In 15 days, some 400 million Europeans will choose between a project ... to build Europe further or a project to destroy, deconstruct Europe and return to nationalism," French President Emmanuel Macron told the gathering.

"Climate, protection of borders and a model of growth, a social model ... is what I really want for the coming years," he said.

On climage change, France and eight other EU countries proposed getting to "net-zero greenhouse gas emissions" by 2050 and the bloc will now debate how to frame and finance any transition to more environmentally-friendly policies.

"Nothing has changed when it comes to divides and different opinions about it," said the chairman of the talks, European Council President Donald Tusk.

"What is new is this very fresh and energetic pressure," he said of youth protests growing in Europe to demand radical action to safeguard the planet. "There is no future for politicians without this sensitivity and imagination."

German Chancellor Angela Merkel refused to endorse the French-led proposal entirely but backed spending a quarter of the EU's next joint budget for 2021-28 on climate and energy efficiency.

A report released today by the World Wide Fund (WWF) and Global Footprint Network sharply criticised the EU, saying its members consumed the Earth's resources faster than they can be renewed.

The leaders pledged to protect the rule of law at a time when the governments in post-communist members Poland, Hungary and Romania stand accused of undercutting democracy.

Divided over issues ranging from democratic standards to migration, the EU is grappling with the prospect of the UK's departure, a wave of populism, and external challenges from China to Russia to the United States.

It is also lagging behind in areas from artificial intelligence to cyber security, and is scrambling to keep alive a troubled nuclear deal with Iran.

But the leaders signed off on a declaration promising to "defend one Europe", "stay united, through thick and thin" and "always look for joint solutions" ahead.

Mr Tusk announced another summit on 28 May, two days after the European Parliament vote, to let the national leaders agree on appointing new people to hold the EU's top roles until 2024.