Police and FBI officials have descended on an apartment building in Stamford, Connecticut where the driver lived.
Teams wearing hazardous materials suits appeared to be preparing to enter the building and bomb squad truck was seen driving to the area.
Residents said they had been evacuated shortly after 5pm local time (10pm UK time).
More top news
Heavy rain and wind for Scotland and northern parts this weekend with an amber weather warning issued and travel disruption expected.
Heavy rain continues to affect Western Scotland and Northern Ireland
A surgeon linked to two deaths and a series of botched surgeries is to return to work despite an ongoing investigation, ITV News understands