Pawel Adamowicz, 53, was taken to hospital, where he is in a critical condition after five hours of surgery.

The 27-year-old suspect, who has a criminal record, has been detained.

He said the Civic Platform party, which led the previous government and had supported Mr Adamowicz's re-election, had wrongfully imprisoned him.

Mr Adamowicz suffered very serious abdominal injuries during the attack. During a five-hour operation, the mayor was given 41 units of blood.

"He remains in a very, very serious condition," one of his doctors said early on Monday. "The coming hours will be decisive."

In a later update on his condition, doctors said Mr Adamowicz was not breathing on his own and a machine was helping to operate his heart and lungs.

What do we know about the attack?

The incident took place at the finale of the annual Great Orchestra of Christmas Charity event, which was attended by hundreds of people.

Television footage showed the suspect, who was released from prison recently, shouting "Adamowicz is dead" and claiming he had been tortured in prison.

Polish police said he had access to the stage using a media badge, and they are now investigating how he obtained it. Polish broadcaster TVP reported that he had been released from prison in December.

President Andrzej Duda said he was informed that "doctors succeeded in reanimating the heart of the seriously injured mayor".

"There is hope but his condition is very difficult," he said on Twitter, calling on people to pray for Mr Adamowicz.

Doctors said his heart was wounded, as was his diaphragm - the muscle between belly and chest which we use to breathe.

Who is Pawel Adamowicz?

Mr Adamowicz is a native of Gdansk, and has been its mayor for 20 years.

People gather in front of the hospital where the mayor is being treated

A graduate of Gdansk university's law school, he is married to a professor there, and the pair have two daughters - one a teenager and one under 10. His wife was in London at the time of the attack and Poland sent a government plane to bring her home, Polish media reported.

His self-written online biography says he helped to organise student strikes in 1988 - a year of mass nationwide strikes against the communist government. Poland would declare a new democratic republic a year later.

In 1990, he became a city councillor for Gdansk, rising to mayor of the city in 1998. He has held the office ever since. His most recent victory was in November, granting him a sixth term which is due to run until 2023.

What has the reaction been?

Blood donors lined up to contribute after news of Mr Adamowicz's massive blood loss were reported.

The stabbing, during an event that raises money for children's hospitals, has shocked Poland, the BBC's Adam Easton in Warsaw reports.

Moments before the attack, Mr Adamowicz posted a picture on Instagram from the stage of the event, where dozens of people were holding white lights.

The popular mayor, a former member of Civic Platform, is seen as a liberal voice and has supported rights for minorities.

Interior Minister Joachim Brudzinski said the attack was "an act of inexplicable barbarism".

Prime Minister Mateusz Morawiecki said on Twitter: "The attack on the life and health of Paul Adamowicz is worthy of the highest condemnation."