Roads were closed around British Prime Minister Theresa May's Downing Street office on Thursday as police investigated a suspicious item.
"Temporary road closures in place around Whitehall whist suspect item assessed," British police said in a Tweet. "Specialist officers are now in attendance."
A Reuters reporter at the scene said police were calmly directing tourists onto neighboring streets.
May was hunkered in 10 Downing St. with close allies on Thursday as she considered whether to give in to relentless pressure to resign, or fight on to save her Brexit plan and her premiership.
May was due to meet senior ministers to discuss her Brexit bill as plans to put it to a vote in Parliament were thrown into doubt.
May's fate looked sealed after the resignation late Wednesday of Cabinet minister Andrea Leadsom, who said she could not support the European Union withdrawal bill that May plans to introduce to Parliament.
Leadsom, as leader of the House of Commons, had been due to announce on Thursday when a vote on the bill would be held.
But Leadsom said she could not support May's Brexit plan because it did not "deliver on the referendum result" that saw voters in 2016 opt to leave the EU.
"No one has wanted you to succeed more than I have, but I do now urge you to make the right decisions in the interests of the country, this government and our party," Leadsom wrote in a resignation letter to May.
The government on Thursday delayed plans for the bill, which is May's fourth and likely final attempt to secure Parliament's backing for her Brexit blueprint.