WATCH: Bus explodes in London during action movie filming

But not everyone knew the reason behind the detonation

A double decker bus has been blown up in the heart of London as part of a stunt for an action film.

Some Londoners were left confused as they saw the bus go up in flames as it travelled along Lambeth Bridge on Sunday.

The Port of London Authority confirmed it was a stunt for a film and that the bridge was closed off.

But it took some people by surprise.

Author Sophie Kinsella tweeted: "Hey film types, next time you blow up a bus on Lambeth Bridge maybe tell us first so children in park aren't freaked?"

Conservative MP for Mid Worcestershire Nigel Huddleston posted a video of the explosion on Twitter with the message: "Anyone worried about the exploding bus on Lambeth Bridge just now? It was just for a movie."

One user responded to the MP's video with the message: "Surprised with current terrorist activities that this got the go ahead."

Mr Huddleston told Sky News: "Some may fear it was for real if far enough away not to see the cameras and crew.

"They did notify locals by putting notices in flats and offices etc. But given the size of the explosion I'm sure many tourists and some locals must have been worried.

"Twitter worked pretty well in clarifying it was for a film pretty quickly. But not everyone is on Twitter."

The controlled explosion was part of filming for a scene in The Foreigner, which stars Jackie Chan and Pierce Brosnan.

The film's producers posted a warning on Twitter about the explosion beforehand which said: "The explosion is controlled and operated by our special effects team."

It added: "Every precaution will be taken to ensure the safety of the people in the area."

However, it looks like some astute commenters notice a blooper int he making:

The film is directed by Martin Campbell, who was behind Bond films Casino Royale and GoldenEye.