BOSTON and surrounding towns remained in a state of lockdown last night as thousands of heavily armed police hunted for the surviving suspect in the deadly Boston Marathon terror bombings.

Authorities said Dzhokar Tsarnaev escaped an overnight shootout in the Watertown district with police that resulted in the death of his brother Tamerlan Tsarnaev – the other man wanted in connection with the bombings. There were warnings the suspect was possibly armed with explosives.

It emerged the suspected bomber posted a message on Twitter eight months ago saying: "Boston marathon isn't a good place to smoke."

Massachusetts State Police spokesman David Procopio said: "Investigators are recovering a significant amount

of homemade explosives" from the scene of the shootout."

Colonel Timothy Alben of the Massachusetts State Police said officers in Watertown were searching "door to door, street to street" for the suspect.

Massachusetts Governor Deval Patrick said there were "continuing developments" in the investigation and that an order to stay indoors remained in place.

Maret Tsarnaev, the aunt of the suspects, said the pair were normal young men who she believed were being set up.

"Give me evidence," she said. "Why doesn't the FBI give me more, if I am asking?

"You have to have a motive first – something that would drive you to some actions. They cannot go crazy or mad or sick just for one day. As far as I know, they are fine."

Hundreds of officers amassed in Watertown, supported by bomb squad robotic equipment and armoured vehicles, giving the quiet town the appearance of a warzone.

Across the greater Boston area almost one million people remained confined to their homes, mass transit systems were suspended, a no-fly zone was imposed and scheduled Boston Bruins and Red Sox games were cancelled.