A junior doctor has described how he "ran to help" victims of the Westminster attack when he heard screaming while off-duty in the area.

NHS doctors, nurses and emergency staff have been called “heroes” for their brave response to the terror attack.

Medics working at nearby St Thomas’s left the hospital and rushed to the scene of the incident outside Parliament and on Westminster Bridge after a man drove a car along a pavement and stabbed a policeman.

Four people died including the wounded officer named as 48-year-old Keith Palmer and the assailant who was shot dead by police.

Jeeves Wijesuriya, the first doctor to attend to the injured, said he entered the police cordon to attend to PC Palmer and the attacker.

“I heard the screaming so ran to help and the police ran me in,” he told Buzzfeed News.

Dr Wijesuriya said emergency services and police were “incredible as we tried to save both the officer and the assailant,“ adding: "We spent some time trying to resuscitate them both."

A medic near Westminster Bridge and the Houses of Parliament, where a police officer was stabbed yesterday (Getty Images)

One of the patients died at the scene and the other at St Mary’s hospital in Paddington, he said.

Liberal Democrat leader Tim Farron told the BBC he had seen “medics run into danger” to help the 29 injured in the attack, which police are treating as a terrorist incident.

He urged people not to “give up on our values and give into fear“, saying there was “lots to be proud of yesterday”.

Spanish teacher Aysha Frade, 43, and a 30-year-old man were also among the victims. Seven people are in a critical condition in hospital.

Neena Modi, president of the Royal College of Paediatrics and Child Health, praised Dr Wijesuriya on Twitter, saying: “We’re proud of you and everyone who stepped up. All sympathies with those affected by yet another senseless tragedy.”

“In the darkest of days, real heroes appear,” said campaign group NHS Million in a tweet that has been shared more than 1,700 times.

And doctor Rachel Clarke wrote: “Amazing NHS doctors and nurses from Tommies [St Thomas’s] – running straight to those in need, regardless of risk to selves. Heroes.”

Dr Tony Joy, of London’s Air Ambulance, who were called to treat victims of the attack, told the BBC: “We were immediately on scene and started to asses the casualties, and looked for information about how many other patients there might be.

“We assessed a number of patients, we were involved in treating several, and tried to support the London ambulance services in any way we could.”

PC Palmer, a husband and father who had served in the Metropolitan Police for 15 years, was outside Parliament when a man armed with two knives entered the gates and stabbed him.

In pictures: Westminster attack Show all 9 1 /9 In pictures: Westminster attack In pictures: Westminster attack An air ambulance lands after gunfire sounds were heard close to the Palace of Westminster in London PA wire In pictures: Westminster attack MPs wait until the situation is under control in Westminster. 'The alleged assailant was shot by armed police,' David Lidington, leader of the House of Commons, told the house. BBC News In pictures: Westminster attack Crowds gather in Westminster after shooting incident, which police are treating as terror attack BBC News In pictures: Westminster attack Police were also called to an incident on Westminster Bridge nearby AP In pictures: Westminster attack Early reports indicate the car, which mounted the pavement on Westminster Bridge and mowed into around a dozen people, was the same vehicle which then rammed into the railings of the Palace of Westminster, just around the corner Reuters In pictures: Westminster attack Security sources described the suspected assailant as a middle-aged Asian man, who is understood to have left the car before attacking a police officer with a seven-to-eight inch knife PA wire In pictures: Westminster attack Police have asked people to avoid the immediate area to allow emergency services to deal with the ongoing incident AP In pictures: Westminster attack One woman has died and a number of others, including the police officer, have been hurt, according to a junior doctor at St Thomas' Hospital Reuters In pictures: Westminster attack At least three gun shots were heard by those inside Westminster, and proceedings in the House of Commons have been suspended AP

Mark Rowley, the Met's top anti-terror officer, said PC Palmer was “someone who left for work today expecting to return home at the end of his shift, and he had every right to expect that would happen.”

Eight people have been arrested in connection with the attack after police searched six addresses.