Two Australians injured in fatal London stabbing attack.

Two Australians are among five people injured and one American is dead after a shocking stabbing attack in central London.

Australian high commissioner to the UK Alexander Downer said two Australians suffered non-life-threatening injuries in the Russell Square attack.

A Department of Foreign Affairs and Trade (DFAT) spokesperson told the Sydney Morning Herald the Australians at this stage can only be identified as a man and a woman.

The spokesperson said the Australian man had already been released from hospital and the injured woman was expected to be released soon.

Police say the attack left one 64-year-old American dead.

The suspect arrested is said to be a 19-year-old Norwegian man of Somali descent.

Assistant Commissioner Mark Rowley said the incident was most likely triggered by “mental health issues”.

“Whilst the investigation is not yet complete – all of the work that we have done so far, increasingly points to this tragic incident as having been triggered by mental health issues,” he said.

The five injured are said to be American, British, Australian and Israeli.

American Darlene Horton, 64, was travelling with her university professor husband as he taught a summer study abroad program.

Horton was killed on the day she and her husband were meant to return home.

Fernando, 40, a paralegal from Brazil, told the Sun he was cycling by when a group of people screamed at him to stop.

“It was a mother and father and two sisters. Then I saw a white lady, in her sixties, slumped against the railings,” he said.

“She had her head in a Spanish woman’s lap, the lady, who was trying to keep her alive by talking to her. They were not related, I think the Spanish family were just passing by.”

“She had been stabbed in the back. She was bleeding.”

Watch a witness describe the scene. Post continues…

Florida State University President John Thrasher told USA today the university simply didn’t have the words to express their sadness.

“There are no words to express our heartache over this terrible tragedy,” he said.

“We are shocked that such senseless violence has touched our own FSU family, and we will do all we can to assist Professor Wagner and his loved ones, as well as his friends and colleagues in the Psychology department, as they mourn.”

The DFAT spokesperson said a second Australian woman was involved in the attack but was not injured.

Police said they received calls about the attack and were on the scene six minutes later.

The suspect was said to have been subdued with tasers.