Police have carried out a controlled explosion and arrested a man outside of Buckingham Palace after he allegedly threw suspected shotgun cartridges onto palace grounds.
The man was arrested just after 7pm local time (4am AEST) after he approached the gates of the palace and "threw a number of items", Metropolitan Police said.
He was arrested on suspicion of possession of an offensive weapon after a knife was allegedly found on him.
Police say he was also found to be in possession of a suspicious bag.
Buckingham Palace said neither King Charles nor Camilla, the Queen Consort, were at the palace at the time of the incident.
Police said roads around the palace had been reopened and some cordons had been lifted following the incident.
Security around London has been heightened ahead of the King's coronation at Westminster Abbey on Saturday.
"Officers worked immediately to detain the man and he has been taken into police custody," Chief Superintendent Joseph McDonald said in a statement.
"There have been no reports of any shots fired, or any injuries to officers or members of the public.
"Officers remain at the scene and further enquiries are ongoing."
The statement added that the incident was not being treated as terror-related.
The sound of the controlled explosion was captured during the broadcast of Conservative MP Jacob Rees-Mogg's show on local news channel GB News.
Mr Rees-Mogg and his guest were about to be evacuated from a demountable building set up near the palace ahead of the coronation when a blast was heard.
"I'm very sorry to say but it is good evening from me for the time being, as I think that was probably a controlled explosion in the background, that's what it sounded like to me," he said.
Earlier on Tuesday, King Charles III met with Australian Prime Minister Anthony Albanese at Buckingham Palace ahead of the coronation.
