Armed police have tasered an intruder who entered the gates of Parliament.
Witnesses described armed police running towards the Carriage Gates and pinning a man to the ground.
Images from the scene show the man pinned to the ground, surrounded by police officers as one points a gun at him.
The man was shot with a Taser, police confirmed.
A spokesperson said: "A man was detained and arrested by Carriage Gates inside the Palace of Westminster on suspicion of trespassing at a protected site, at around 11.55hrs."
The BBC's Laura Kuenssberg said that the intruder had been taken away in a police van.
Today's incident was not terror-related, police said.
It’s the same location as the Westminster attack last year.
Conservative MP Penny Mordaunt wrote on Twitter: "Always in awe at the professionalism, courage and dedication of the police who guard the Palace of Westminster. Thank you all."
A Met Police spokesman said: "A man arrested inside the grounds of Palace of Westminster this morning remains in custody.
"At around 11.55am, a man tried to gain entry to the grounds of the Palace of Westminster via Carriage Gates, and ran towards officers posted there.
"He did not comply with officers' requests to stop. A Taser was deployed.
"The man was subsequently arrested on suspicion of trespassing at a protected site, and taken to a police station where he remains.
"The arrested man will have a mental health assessment.
"The investigation will be led by officers from Parliamentary and Diplomatic Protection. Enquiries into the circumstances continue."
