The FCO has updated its travel advice for the US warning of a high risk of tornados, severe storms and flooding across a number of eastern, central and southern states.
Extreme weather has produced hundreds of tornadoes in eight states including Colorado, Ohio, Iowa, Nebraska and Illinois.
The severe weather has extended beyond the Midwest. Tornadoes were confirmed in eastern Pennsylvania and the National Weather Service issued a tornado warning for parts of New York City and northern New Jersey.
“Areas of concern” now extend from St Louis to Dallas and from Pittsburgh to New York City, and from Philadelphia to Washington DC.
Up to 55 twisters hit a path from Pennsylvania to Colorado on Monday, and more followed on Tuesday when after a large tornado headed to the western edge of Kansas City.
It is the most intense periods of storm activity in nearly 40 years.
Kansas City International Airport temporarily suspended flights and forced travelers and employees to take shelter in parking garage tunnels for about an hour.
The tornadoes have claimed the life of at least one man – an 81-year-old resident of Celina, Ohio – who died when a car was thrown into his home.
The FCO travel advice states: “There is currently a high risk of tornados, severe storms and flooding across a number of eastern, central and southern states. You can check forecasts and weather warnings on the US National Weather Service website and learn more about what you should do during and after a tornado.”