Large cities around the world have lit up their landmarks with the union flag in solidarity with London following the lone-man terrorist attack by Westminster Palace.

In Tel Aviv, its city hall bore the red, white and blue union flag on one side of the building, with the Israeli flag on the other.

Paris, which has been the centre of larger-scale terrorist attacks in recent years, switched off the lights at the Eiffel tower to show its support for London following the attack. Paris' mayor, Anne Hidalgo said the tower would turn off its twinkling lights at midnight.

On the domestic front, Birmingham lit up its library in the Union Jack colours.

"The @LibraryofBham lit to show Birmingham's solidarity with London. Our thoughts are with everyone affected by today's #Westminster attack," tweeted John Clancy, the head of the Birmingham City Council.

"Tonight the Second City #brum stands shoulder-to-shoulder with #London following today's #Westminster attack," he tweeted.

Social media also made its support clear with various backdrops in sympathy of the attack. Facebook launched its safety check feature in London to allow people to mark that they are safe as a status update that is then published for their friends and family to see.

La tour Eiffel/Twitter

Facebook's The Attack in Westminster safety check arrived just as the hashtag #PrayforLondon started trending on Twitter. The safety check feature launched by Facebook was used not just in major terror attacks in Paris, Berlin and Pakistan but also during natural disasters.

From #We are not afraid through #LondonIsOpen, #PrayforLondon and #LondonStrong, users of social media sent sympathy and support. One hashtag, #ThinBlue Line, paid tribute to fallen police officer PC Keith Palmer.