Editor's note: For the latest on this developing story, click here or go to Telemundo Nueva Inglaterra to read the story in Spanish.
Several agencies responded Thursday evening to the Merrimack River near the Whittier Bridge in Massachusetts for reports of several people in the water, and officials later confirmed that one woman had died and her 6-year-old son remained missing.
Around 7:10 p.m., the Amesbury Fire Department received a report for people in the water in distress, according to a joint press release from Newburyport Fire Chief Christopher LeClaire and City Marshal Mark Murray.
Amesbury police and fire departments, as well as state police, responded and found several people in the water.
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Six people -- a mother and father with their four children -- are believed to have been fishing along the edge of Deer Island in Newburyport when two of the kids went into the river, LeClaire said.
The mom went after them to bring them back to shore, and she was assisted by a nearby fishing vessel. The mom successfully got her 7-year-old daughter onto the boat, but she was unable to get herself up, LeClaire said.
The woman, whose name is not being released at this time, went under water and did not resurface. Rescuers located the mom and brought her out of the water, but she was unresponsive and not breathing, the fire chief said. CPR was administered on scene before she was taken to Anna Jaques Hospital in Newburyport where she was pronounced dead.
The woman's 6-year-old son remained missing Thursday night. All other family members were accounted for, and taken to a local hospital where they were doing okay, the fire chief said.
Officials believe the boy was on land when he slipped into the water. Discussing ongoing search efforts late Thursday night, LeClaire said they do believe the boy is in the water, and their search efforts will continue throughout the night.
Rescuers from throughout the region -- all area departments, harbormasters, coast guard, and police departments -- are assisting in the search, and all resources were still in the water as of 10 p.m. Thursday.
LeClaire noted that everyone is aware of who they are trying to find.
"We know that we are still searching for a a 6-year-old boy so we will continue to search until we've exhausted all possibilities," he said. "We'll continue to search into the daylight and we'll work with the Coast Guard and other assets to make further decisions from there."
The fire chief also acknowledged that the chances of recovering the boy are dwindling as time passes.
"We're still continuing to search in hopes that we'll recover the 6-year-old. Again as time goes, it becomes less and less likely and we'll be in a recovery mode," he added. "But we'll continue to put our best efforts forward to see if we can locate the child."
Massachusetts State Police confirmed they were requested to assist around 7:18 p.m. after multiple people were swept into the Merrimack River near Deer Island at the Amesbury/Newburyport town lines. Police also confirmed one person had died in the incident.
To assist in the search for the missing boy, state police sent a helicopter, as well as boats and divers from their marine unit that launched from Cashman Park in Newburyport. Troopers also responded to the Whittier Bridge on Interstate 95 and the nearby area.
State police said their helicopter, boats and dive team were still searching for the boy as of 11 p.m.
Helicopters and boats will continue to refuel and keep the search going throughout the night, LeClaire said.
Deer Island is an island in the Merrimack River on the Amesbury/Newburyport border. LeClaire described the conditions as typical when asked Thursday night, noting the river's quick pace and rocky ledge.
"Typical Merrimack River conditions. Tide at the time was just the end of high tide, the river can be moving at a quick pace. The area is known for fishing and swimming and other recreation, it is a rocky ledge in the river," the fire chief said. "It is quite heavily used this time of year. People are known to fish along the edge along Deer Island."
Authorities originally said they received reports that a boat had run aground in the area, or there was some kind of boating accident, but LeClaire clarified later Thursday that they do not believe a boat was involved.
While the report initially came into the Amesbury Fire Department Thursday, Newburyport Fire has assumed responsibility for the call, officials said. Numerous mutual aid partners were assisting on scene including, Massachusetts Environmental Police, the United States Coast Guard, Massachusetts Department of Fire Services, Cataldo Ambulance, Seacoast Chief Fire Officers Mutual Aid District, Newbury Harbormaster and Amesbury Police.
The Amesbury, Merrimack, Salisbury, Haverhill and East Kingston, New Hampshire, fire departments are also providing aid, and Massachusetts State Police assigned to the Essex District Attorney's Office responded to the scene, as well.
Aerial footage from NBC10 Boston's SkyRanger helicopter showed the massive rescue response to the scene.
Countless first responder vehicles could be seen parked along the bridge, while several boats were in the water, and state police and Coast Guard helicopters were flying overhead.
NBC10 Boston talked with one woman who lives nearby and she said her husband also got into his kayak Thursday evening to help look for the child after he realized what was going on.
"My husband was out here with the dog, and I was like, what's taking so long? And then all of a sudden he's screaming at me, and he's talking about a woman and CPR," said Sue Bajko. "I came out and two fishermen came on our dock here in their boat and they pulled the woman and her daughter out of the boat and did CPR."
The search for the woman's son remains active and ongoing, and an investigation is underway.