There are reports of police activity near the US Embassy in Mayfair.
The FT has reported "significant police activity" with surround streets closed to traffic and workers in nearby office buildings being told to stay indoors.
The Metropolitan Police said they were called out to reports of a suspicious vehicle but the incident has since been stood down.
There is a heavy police presence on the streets of the capital today following a terrorist attack at Westminster yesterday afternoon.
The incident, in which an attacker drove along the pavement of Westminster Bridge and then stabbed a police officer, left four people dead. The assailant was shot by police.