A convicted murderer is at large after armed men helped him escape during a hospital visit in Liverpool.

Detectives investigating the escape of Shaun Colin Walmsley - described as "highly dangerous" - are appealing for the public’s assistance.

He fled from outside Aintree University Hospital as he was getting into a car with prison officers.

Merseyside Police said two men believed to be armed with a gun and a knife assisted his escape.

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A picture of the gold-coloured volvo used by the two men who helped him escape

Officers said the men threatened guards and demanded they release Walmsley before making off in a gold-coloured Volvo.

Mayor of Liverpool Joe Anderson said he is "angry and incredibly shocked" by the "serious security breach" and is waiting for a full briefing into what happened.

He said: "We have to call for an inquiry into what has gone on and what has happened - I am going to write to the Home Secretary.

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Liverpool Mayor Joe Anderson (Peter Byrne/PA)

"This is somebody who is a convicted murderer who could well be in my city or anywhere else.

"We don't know whether he has got out to be part of any drug disputes in the city."

Mr Anderson said it is a “tense time” in the city following recent murders and it looked like Walmsley had planned the escape well in advance.

At about 3.05pm yesterday, Walmsley escaped from his guards outside the Aintree hospital as they were leaving following the medical appointment.

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Shaun Walmsley fled from outside Aintree University Hospital in Liverpool (Dave Thompson/PA)

Walmsley, 28, was remanded in custody at HMP Liverpool after being sentenced to life imprisonment in June 2015 with a 30-year tariff for the murder of Anthony Duffy.

Detective Superintendent Natalie Perischine, said: "An investigation into the full circumstances of the incident is ongoing and Merseyside Police is working with the Ministry of Justice and other forces across the country to establish Walmsley's whereabouts so that he can be returned to prison.

"Walmsely is a highly dangerous individual, who was convicted of a vicious and savage murder of 33-year-old Anthony Duffy who was stabbed multiple times during the attack which robbed him of his life in 2014.

"He took the life of this young man in a frenzied attack and in doing so ruined the lives of his victim's family and friends.

"We will be relentless in our pursuit of Walmsley and the men who helped him to escape and we need the public's help to find him and put him back behind bars."

Detectives are advising the public not to approach Walmsley if they see him as he could be in the company of the others who helped him escape and they are believed to be armed.

Officers urge anyone who has seen Walmsley or knows where he is to contact them on 999 or call Crimestoppers anonymously on 0800 555 111.