Transport for London (TfL) is warning of severe delays amid road closures following an attack in which four people have been confirmed dead and at least 20 have been injured.
All approaches to Parliament Square remain closed.
Northumberland Ave and Millbank are also closed and Westminster Bridge is closed westbound at York Road.
Victoria Embankment has been closed southbound at Northumberland Avenue and Northumberland Avenue eastbound from Trafalgar Square is also closed to traffic.
Whitehall has been closed southbound at the junction with Trafalgar Square.
Pall Mall has been reopened eastbound at St James Street.
Lambeth Palace Road has been closed northbound at the roundabout by Albert Embankment.
Westminster Bridge Road is closed northbound at Baylis Road.
All traffic is being diverted by police.
Although slow, traffic is moving on Albert Embankment from Vauxhall Cross with tailbacks to Lambeth Road.
The Vauxhall Cross Gyratory is open but traffic is slow moving with traffic queuing over Vauxhall Bridge back on Vauxhall Bridge Road to Victoria.
Traffic is heavy northbound on Blackfriars Road.
If you are looking to cross the river, Waterloo Bridge remains open, as does Vauxhall Bridge.
This image from Google Traffic shows the current traffic situation, on surrounding roads.
Westminster Tube station remains closed, but here are a few alternatives you could use.
From Westminster, it's a 17 minute walk to Waterloo station, or a 21 minute walk to Green Park instead, both of which will give you access to the Jubilee Line.
Alternatively, Embankment is a 10 minute walk from Westminster station which will give you access to the Bakerloo, Northern and District and Circle Lines - or add on an extra nine minutes to your walk to get to Temple and avoid as much traffic as possible.
Buses remain delayed or on diversion.
There is also severe disruption to river services due to a police river closure.
There will be no RB6 service until further notice and the RB1 and RB2 services are also affected.
Services will not be calling at Embankment, Westminster or London Eye piers.
TfL is advising those travelling to check their route before setting out.
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