A road in the centre of London's government district, near Prime Minister Liz Truss's Downing Street office and residence, was closed on Tuesday due to a suspicious package, police said on Tuesday.
Whitehall, between the Houses of Parliament and Trafalgar Square, is also home to several government departments including the foreign ministry, the Cabinet Office and the Ministry of Defence.
London police said on Twitter they had been called at 11.42am (1042 GMT) to reports of a suspicious package, reports Reuters.
"Officers are in attendance and a cordon is in place as a precaution. The item will be assessed by specialist officers. Please avoid the area," the police said.
A government official said some of the government buildings along Whitehall were being emptied. A Reuters reporter said hundreds of people were gathered at Horse Guards Parade, behind Downing Street.