The scene of two explosions at the finish line of the Boston Marathon that killed three people and injured more than 140 remains closed as city, state and federal law enforcement agencies investigate.

The area around Copley Plaza was blocked to vehicles and pedestrians by yellow police tape early today as the city awoke the day after the explosions.

The crime scene was secured by police and the National Guard.

Highway exits to the area from the Massachusetts Turnpike and Storrow Drive were closed to traffic, and police were urging commuters to find alternate routes.

The MBTA is running as normal, but Green Line trolleys are not stopping at the Copley Station subway stop.

Two bombs exploded seconds apart at about 2:50 p.m. Monday as many runners were crossing the finish line.