Witnesses have described a pickaxe-wielding attacker going on a rampage at a hospital, leaving two people injured.

Gareth Browne, a steeplejack contracted to repair the chimney at Central Middlesex Hospital, in north-west London, said he saw the alleged attacker chase two men who managed to escape on Wednesday.

He then screamed at Mr Browne, “get out of my f****** way – this is none of your business”, before running into the hospital.

Armed police were called to the site just before 1.20pm after two people were attacked, one of whom suffered life-threatening injuries.

The suspect himself also had life-threatening wounds that police believe were self-inflicted.

Mr Browne said: “He came out of the side of the building waving a pickaxe, chasing two lads about.

“I approached him and asked if he’s OK and he said ‘get out of my f****** way – it’s none of your business’.

“So I stepped out of his way and he went back into the hospital waving that pickaxe around.

“Another maintenance boy came along and said ‘he’s just stabbed somebody – get away from this place’.

“He was just going on a mad rampage.”

Visitors and patients at the hospital were temporarily locked down as police scoured the building, eventually arresting a man outside.

The attack is not being treated as terror-related, and officers are not looking for any other suspects.

Police will remain at the hospital as an investigation is carried out.

Amie Ferris-Rotman, who was visiting the hospital dialysis unit with her father, told Sky News that police checked the area where they were before locking them in a nurses’ room for about 45 minutes.

She said: “All the dialysis patients were quite freaked out.

“And at one point those who were about to go on to dialysis were put on wheelchairs and brought into a room, which is where we were as well, and they were locked in.”

The hospital reopened at about 4pm, with services running as normal.