This article is being updated in real-time as the story develops.
Update 8:45 p.m.: Police report they have successfully apprehended the second suspect and he is now in custody.
Update 8:31 p.m.: NBC News reports that a negotiator is now on the scene in Watertown.
Update 8:22 p.m.: A CNN reporter said law-enforcement officers told the suspect to "come out on your own terms" and "come out with your hands up."
Update 8:07 p.m.: The suspect is exhibiting "negative movement" while laying on his back, according to information distributed via Boston police scanner. CNN reports "a number of flashbang grenades" have been used. Reports emerge that the suspect was found via a heat-seeking device on a helicopter.
Update 7:53 p.m.: Information distributed via Boston police scanner stated that the suspect was not moving and that there had been a fire on the boat at one point, but it was unclear whether the boat was still burning. There was also discussion of flashbang grenades "lighting up" the boat and more heard on the scanner.
Boston Marathon bombing suspect Dzhokhar A. Tsarnaev was reportedly cornered in a boat by law-enforcement officers following a series of gunshots that were heard Friday shortly before 7 p.m. EDT in the Boston suburb of Watertown.
The gunshots were heard by CNN reporters, and the network then showed footage in which the rapid shots could be heard. Both the Boston Globe and CNN reported that a source said the bombing suspect had been cornered.
The Globe initially reported that the suspect had been pinned down by police, but the newspaper changed its story shortly thereafter to say that sources said he was cornered in a boat in a Watertown backyard.
CNN reported that police said that the suspect has "something out of the ordinary" that may be a bomb or other weapon, which reportedly has police concerned for the safety of officers near the suspect.
Police told reporters on the scene shortly before 7:10 p.m. to ignore their decision to lift the lockdown on the Watertown neighborhood earlier in the day, and that folks in the area should stay inside their homes.
Shortly thereafter, CNN announced live that a police source had told it that the suspect was cornered in a structure of some kind and that officers were deploying tear gas in an effort to either draw the suspect out or get the individual to pass out.
Immediately following the gunfire, a large number of law-enforcement vehicles and officers headed in the direction of the shooting.
The world's eyes had been focused on Watertown almost all day Friday as authorities swept the neighborhood in search of the 19-year-old Boston Marathon bombing suspect.
The entire suburban community was locked down for most of the day by authorities, who urged all Boston-area residents to remain inside their homes until notified otherwise, as Tsarnaev is considered by law enforcement to be "armed and extremely dangerous," as FBI Special Agent Rick DesLauriers said this week.
Tsarnaev's 26-year-old brother Tamerlan Tsarnaev was killed overnight in a wild altercation with law-enforcement officers that left one Massachusetts Institute of Technology police officer dead and precipitated the massive manhunt.