A busy road in south London was closed by armed officers after police arrested three men.
Police cordoned off a stretch of Blackfriars Road from the junction with St George's Circus after a security alert at about 1.45pm.
Scotland Yard said police had stopped a car in Blackfriars Road and arrested three men on suspicion of theft of a motor vehicle.
Social media users said they had been told to stay inside and keep away from windows by officers.
<blockquote class="twitter-tweet" lang="en"> <p dir="ltr" lang="en">Armed police in Blackfriars Road <a rel="nofollow" target="_blank" href="https://t.co/WC2Yh8JVkU" class="body-link" data-vars-item-name="BL-3120171-https://t.co/WC2Yh8JVkU" data-vars-event-id="c23">pic.twitter.com/WC2Yh8JVkU</a> — London SE1 (@se1) <a rel="nofollow" target="_blank" href="https://twitter.com/se1/status/668075891268919297" class="body-link" data-vars-item-name="BL-3120171-https://twitter.com/se1/status/668075891268919297" data-vars-event-id="c23">November 21, 2015</a>
Nicola Asuncion tweeted: "We've currently got Blackfriars Rd closed off and police everywhere."
She added: "Police had two and three men held to one side, everyone told to move back or go indoors."
Scotland Yard did not expand on the reasons for the large police presence and road closure.
A police spokeswoman said: "At 1.44pm on Saturday, 21 November, officers stopped a vehicle on Blackfriars Road at the junction with St George's Circus.
"The occupants of the vehicle - three men - were arrested on suspicion of theft of a motor vehicle.
"They currently remain in custody at a south London police station."
Roads began to reopen at about 3.30pm.
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