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
Firms that fail to address the pay gap between male and female employees with be listed in new league tables.
John Kerry says US and Russian diplomats have agreed to implement a "cessation of hostilities" in Syria
A young man dramatically rescued by the Turkish coastguard from a sinking boat has spoken of his ordeal.