Icy conditions and accidents have closed roads and bridges in and around Philadelphia, including a pile-up involving at least 20 cars on a major artery that serves the city's western suburbs.

Interstate 76 was closed in both directions after a series of cars slammed into one another amid freezing rain this morning. The accident occurred before 7am local time in the westbound lanes near the Gulph Mills exit. The extent of any injuries was unclear.

Accidents caused the closure of Interstate 95 in both directions in parts of Philadelphia, and all four bridges linking the city and New Jersey were closed as workers applied salt.

A freezing rain advisory is in effect in the area until 10am, but temperatures were forecast to rise to about 5C later in the day.