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Knife-wielding man stunned by police outside Buckingham Palace

Police use a stun gun on a man who puts a knife to his throat after trying to enter the gates at London's Buckingham Palace . NBCNews.com's Dara Brown reports.

A man holding a knife to his neck was immobilized with a stun gun by police outside London’s Buckingham Palace during Sunday’s Changing of the Guard ceremony.

Smartphone video of the incident, published on news sites including the Daily Telegraph, showed the man being brought to the ground by the police weapon.

He was immediately arrested and is in custody, according to a Metropolitan Police spokesman, although it is not yet clear if he will be charged with any offense.

The incident happened at 11:55 a.m. local time (6:55 a.m. ET) on the street outside the palace gates in the west end of central London.

It was witnessed by hundreds of tourists who had gathered to see the 45-minute Changing of the Guard ceremony.

The queen and her husband, Prince Philip, were at their rural home in Sandringham, Norfolk, at the time.

Buckingham Palace said it would not comment, according to ITV News.