It happened on Tuesday evening in Gillingham - near Brompton Barracks, headquarters of the 1 Royal School of Military Engineering Regiment.

A woman said she heard a "huge scream", ran to her window and saw the attacker stabbing the soldier on the ground before escaping on a moped.

Sky News understands it's not being treated as a terror incident.

Kent Police said the victim - in his 40s - is in a serious but stable condition after being airlifted to hospital.

Police were called to the scene around 5.55pm, with a 24-year-old local man arrested at about 6.30pm in Rochester.

Another witness said he saw a man in "cream camouflage" motionless on the ground after the attack.

"I came out on the street, went over to the corner. It was a minute and a half after the incident, there were already 10 people around the body," said Alex Reynolds.

"The body was lying there and not moving."

Mr Reynolds and others have described a moped speeding away and someone trying to chase it in a car.

Attacker 'seemed calm'

A third witness - who didn't want to be named - told Sky News she heard "lots of car horns and men shouting" and assumed it was road rage until she "heard a woman screaming".

"She sounded like a woman who was hysterical. She came this way and said 'my husband's been stabbed, is there a first aider?'"

The witness said the attacker had a helmet on but "seemed calm" and "wasn't even breaking a sweat".

The incident comes 11 years after Lee Rigby was murdered near the Royal Artillery Barracks in Woolwich, southeast London.

The prime minister said he was "shocked and appalled".

Writing on X, he added: "All our thoughts are with the soldier, his family and our Armed Forces community, who serve to keep all of us safe. I wish him a swift recovery."

Home Secretary Yvette Cooper said she was getting updates from police.

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The head of the army, General Sir Roly Walker, said it was a "horrific and unprovoked attack on an officer".

"Our armed forces make extraordinary sacrifices to defend our nation and deserve to be respected," he said.

"My thoughts and best wishes are with him and his family. They have the full support of the chain of command as they recover from this horrendous incident."

Brompton Barracks trains soldiers in construction and engineering skills before their first posting to an operational unit.

It's been the home of the School of Military Engineering since 1812.