Kent Police arrested a 24-year-old man late Tuesday on suspicion of attempting to murder the soldier, a man in his 40s, on the street in the town of Gillingham, southeast of London.

Emergency responders airlifted the victim to hospital, with his condition described Wednesday as serious but stable.

Prime Minister Keir Starmer said he was "shocked and appalled" by the incident.

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

In an update, Kent Police said officers had arrested the local man in nearby Rochester within half an hour of being called to the scene of the attack, near the British Army's Brompton Barracks.

He was reported to have left the scene on a motorcycle, and "a number of knives" have been seized, the force added.

"The motivation for the attack is currently unknown and forms part of our ongoing enquiries, although we are exploring the possibility that it may be mental health-related," Acting Chief Superintendent Richard Woolley said in a statement.

"We are also investigating any possible links between the location and the suspect," he added, noting investigators do not believe anyone else was involved.

"There is no further information at this time to suggest there are any wider threats to the local community including members of the armed forces," Woolley said.

The attack has echoes of the 2013 murder of British soldier Lee Rigby, who was hacked to death by two Islamist extremists on a southeast London street.

Earlier on Tuesday, Anjem Choudary, the radical preacher whose proscribed Islamist group inspired that pair, was found guilty by a UK jury of directing a terrorist organisation.

A British Army spokesman said: "We're very sorry to confirm that a soldier has sustained serious injuries in an attack.

A witness who rushed to aid the wounded soldier told The Sun tabloid that the attacker had been on a moped before running at the victim and stabbing him repeatedly.

The soldier had "wounds all over his body", according to the witness.

"Blood was everywhere as I tried to apply pressure to his wounds until the police arrived," the witness added.

"When the guy's (soldier's) wife came out and started trying to pull the guy off he didn't even try to hurt her."

Defence Secretary John Healey called the attack "shocking" and said his thoughts were with the soldier and his family.