BRUSSELS (BLOOMBERG) - Chancellor Angela Merkel said the European Union faces "a whole array of unsolved problems" at what was likely her final summit, striking a sombre tone that contrasted with a celebratory send-off by the bloc's leaders.

"I leave the European Union in my role as chancellor in a situation where there is a lot to worry about," Merkel told reporters in Brussels on Friday (Oct 22) following the two-day meeting.

The outgoing German leader cited a fight with Poland over its respect for the rule of law, the failure of EU leaders to reach a comprehensive approach on migration, and the region's competitiveness with China, as issues that will make the EU "vulnerable" to the outside.

Hours before, former president Barack Obama delivered a video tribute to Merkel, with European Council President Charles Michel calling her "a monument."

Future summits will be like "Rome without the Vatican or Paris without the Eiffel Tower," he said, according to an account from an official at the meeting.

The chancellor, the bloc's longest serving leader, logged her 107th European Council meeting since taking office in November 2005.

With German Social Democrat Olaf Scholz aiming to wrap up coalition talks and succeed Merkel by early December, Merkel's two-day visit to the Belgian capital is probably her last to conduct official business.

Obama - whose appearance was the subject of intensive back room negotiation, according to an EU official - was also effusive.

"Thanks to you, the centre has held through many storms," he said.

The 44th US president said he was "happy to become your friend."

A video presentation for the gathered leaders included clips of Merkel's first visit to the council in December 2005, greeted by British Prime Minister Tony Blair and receiving a hand kiss from France's Jacques Chirac.

Usually reticent of such public praise, Merkel was eager to move on to matters at hand - a wide-ranging discussion on migration and protecting the bloc's external border with Belarus.

"Merkel was uncomfortable with all the praise she received; she prefers to talk about the content rather than about herself," Dutch Prime Minister Mark Rutte said after the meeting.

Merkel ignored a final question on how she found a gift from the council - a replica of the egg-shaped building where the Council meets, which many observed resembles her trademark rhombus hand gesture. Instead, she stood and left.

"That was the last question," her spokesman, Steffen Seibert, said.