A far-right German MP has been seriously injured in a 'politically motivated' gang attack in the north of the country.

Frank Magnitz, who leads the Bremen-branch of the anti-immigration Alternative for Germany (AfD), was assaulted in the city centre on Monday afternoon.

The AfD party published a photo of Magnitz lying injured on a hospital bed, claiming three masked men had hit the politician 'with a piece of wood' and fled the scene.

Party leader Joerg Meuthen said the 66-year-old was 'beaten almost to death' in a 'cowardly and sickening' attack.

The assault on Magnitz drew condemnation from across the German political spectrum, including from Chancellor Angela Merkel.

Attacked: Far-right Alternative for Germany (AfD) published photo of MP Frank Magnitz in hospital after allegedly being attacked by three men in Bremen, northwest Germany

Anger: AfD representatives as well as opposition politicians have slammed the 'cowardly' attack on Mangitz, who is the local leader for the party in Bremen

Blood is seen on the ground where Frank Magnitz was attacked in Bremen yesterday

Bremen police said they believe the attack was politically motivated and called for witnesses to the incident, which took place around 5.20pm on Monday near a theater in central Bremen.

Magnitz was beaten over the head with a not officially identified object, by at least three men wearing dark clothing and hoods or hats, who then fled, police said.

Two construction workers who were loading a car nearby found him lying on the ground and called an ambulance

'They hit him with a piece of wood until he was unconscious and then kicked him on the ground,' AfD said in a statement, adding that 'today is a dark day for democracy in Germany.'

The party said Magnitz was ambushed after he left a Bremen newspaper's new year's reception.

AfD co-leader Alexander Gauland speaks during a press conference in Berlin today, where he claimed other parties were to blame for the attack as they compared his party to the Nazis

Police officers stand close to a theatre in central Bremen where Mr Magnitz was found lying unconscious after being beaten over the head

Mr Magnitz had reportedly been attending a new year's reception at a Bremen newspaper when he was attacked near this theatre

'It was clearly an attempt to murder Mr. Magnitz,' AfD co-leader Alexander Gauland told reporters in Berlin.

'This is the result of the ostracism and agitation AfD faces,' he said, suggesting other parties were partly responsible for the attack because they had compared AfD to Adolf Hitler's Nazi party.

Magnitz is associated with the extreme right of the party, including its firebrand leader in the eastern state of Thuringia, Bjoern Hoecke.

Magnitz told the dpa news agency he had been told he would need to remain hospitalized until the weekend and had little memory of the attack.

He added that while he had received threats, he hadn't considered any of them concrete.

Chancellor Angela Merkel led cross-party condemnations of the assault, as her spokesman Steffen Seibert wrote on Twitter that the 'brutal attack' was 'to be condemned sharply'.

'Hopefully the police will succeed in catching the perpetrators quickly,' he wrote.

AfD leader Joerg Meuthen tweeted that Magnitz was 'beaten almost to death' in a 'cowardly and sickening' attack.

Johannes Kahrs, an MP from the Social Democrats, junior partners in the ruling coalition, said 'violence is never acceptable' and that 'extremism in any form is rubbish'. He wished Magnitz a quick recovery.

Two workers loading a truck close to the scene of the attack found Mr Magnitz and called an ambulance (pictured, police officers inspect the scene)

Mr Magnitz told police that he had received threats in the buildup to the attack, but didn't consider any of them concrete

An alleyway leading to the theatre which is where Mr Magnitz was attacked on Monday night

Cem Ozdemir of the opposition Greens party said he hoped those responsible could be 'found and convicted soon' and that, even against a far-right party, 'nothing justifies violence'.

'Those who fight hate with hate only allow hate to win in the end,' said the politician of Turkish origin.

AfD is represented in all of Germany's 16 state parliaments. It entered the national parliament in 2017 and is currently the biggest opposition party there. It views the country's established political parties with contempt, and the feeling is mutual.

The party took 10 percent of the vote in Bremen in the 2017 national election, below its nationwide result of 12.6 percent.

Bremen is not considered an AfD stronghold, unlike three states in Germany's ex-communist east that hold regional votes in September and October.

The party claims there have been 'hundreds' of attacks against its officers and members since its founding in 2013.

Last week, an explosive device detonated in a rubbish bin damaged an AfD office in Saxony. Three suspects were detained.

And last weekend in Lower Saxony, the home of a local AfD politician was targeted with graffiti and a party office was attacked with a paint bomb.