A number of road closures are in place while emergency services deal with the incident, the Metropolitan Police said on Twitter on Monday afternoon.
A controlled detonation has reportedly taken place in Parliament Square, London.
Details of an ‘alleged bomb threat’ had been shared on social media.
Police and emergency services remain on the scene, near Westminster Abbey.
Westminster Police tweeted: ‘We are at currently in the vicinity of #Westminster Abbey dealing with an ongoing incident involving what is believed to be a suspicious vehicle.
‘A number of road closures are in place while emergency services deal with the incident.’
Nearby buildings have reportedly been evacuated amid the incident.
Spectator reporter James Heale tweeted: ‘Parliament Square has been closed off over an alleged bomb threat, one staffer reports seeing the “little robot driving around.”‘