Update: This appears to be a carjacking gone bad in the area of Cambridge. The New York Times reports that the two individuals engaged in a shootout with police behind a black Mercedes before. At that point, one suspect was detained while another fled in an SUV. This incident came hours after a shooting at MIT which left one police officer dead.
Police were involved in the pursuit of at least one suspect who appeared to be on foot according to the scanner, which is being broadcast live.
The bomb squad was called, after there were reports of unidentified packages in the road. Following that, the scanner warned all units have been instructed to power down all cell phones for fear of explosions. The police officers indicated that there might be multiple devices.
This situation is extremely fluid and rapidly developing. Details are changing almost every minute, will update as much as possible.
Please refer to the posts above this for the most up-to-date information.