Citizens all over Boston have been told to stay indoors as police search for a suspect of the Boston marathon bombing.

Police cornered two suspects in the early hours of the morning where an exchange of gunfire critically injured one police officer and killed one suspect, Tamerlan Tsarnaev, 26.

His brother and second suspect, Dzhokhar Tsarnaev 19, escaped and has sparked a city-wide lockdown for Boston. All public transport has been suspended as law enforcement agencies work together to find the ‘armed and dangerous’ suspect.

Massachusetts State Police tweeted: “Do not answer the door, stay away from windows, [and] keep doors locked.”

Just hours after the FBI released photos of the suspected brothers, Sean Collier, a 26-year-old university police officer was shot dead at around 10:48 whilst investigating a robbery at a convenience store on the campus of the Massachusetts Institute of Technology, less than 2 miles from the location of the marathon bombing.

Witnesses describe a ‘war zone’ of explosions and gunfire as the shootout critically wounded one suspect and injured another law officer in the local suburb of Watertown.

The suspect was later pronounced dead upon arrival to Beth Israel Hospital, Boston. The injured police officer remains in surgery.

Since then, local and national police enforcement agencies have been involved in a door-by-door search of Watertown, radiating from the neighbourhood of the fire fight.

Speaking with CBS News, the uncle of the suspects, Ruslan Tsarni has said ‘they have brought shame’ on a family that had ‘nothing to do with them’.

In a press conference, Mr Tsarni said: “For the sake of the family hand yourself in.”

The Tsarnaev brothers are believed to have moved to America in 2001, originating from the Russian Republic of Chechnya.