Public transportation in Boston was shut down Friday morning and some neighborhoods and towns were in total lockdown as police searched for the second of two men believed to have been involved in the marathon bombings earlier this week.

All services on the Massachusetts Bay Transportation Authority were immediately suspended authorities announced and the residents of the city’s western suburbs, including the neighborhoods of Watertown, Allston-Brighton, Cambridge, Belmont and Newton, were asked to remain in their homes.

Designated portions of the MBTA system might open up again later on Friday, Massachusetts Emergency Management Agency undersecretary Kurt Schwartz said.