Breaking: Westminster is in lockdown after gunshots fired

A major security alert is under way at the Houses of Parliament in London after gunfire was heard close to the Palace of Westminster.

The building is currently in lockdown, and there are unconfirmed reports pouring in that a man armed with a knife has been shot by a police officer.

Reuters reports that "a dozen people" have been injured on Westminster Bridge.

London’s Metropolitan Police confirmed they were responding to a “firearms incident” on Westminster Bridge.

There are suggestions that some people may have struck by a vehicle.

At least three gun shots were heard by onlookers.