MONTREAL -- Read the updated story here: Montreal mayor, fire department pay tribute to firefighter who died during rescue operation

A rescue mission got underway Sunday for a firefighter who fell into the St. Lawrence River after a boat carrying people from a previous rescue mission capsized near the Lachine Rapids. 

The boat reportedly sank at around 7:30 p.m. 

About half an hour before, four Montreal firefighters responded to a distress signal from another boat in the area. 

After picking up the two people who called for help, the rescue boat itself capsized. 

While it remains unclear why the accident happened, rescue workers were able to recover everyone on board except the firefighter, who remains missing.  

"So the people that they rescued, they went in the water, along with the firefighters," said Longueuil Fire Division Chief Stéphane Difruscia. "But now, all those people are accounted for, except for one firefighter."

Rescue teams from the Montreal police (SPVM), the Surete du Quebec (SQ), the Coast Guard, as well as firefighters from Montreal and Longueuil took part in the search. An SQ helicopter was also on the scene. 

"I don't have any information about the condition [of the boat]," said Montreal Fire Chief Louise Desrochers.

"But of course, we're talking about the Lachine Rapids, so the water is really moving around there."

Firefighters asked that the public avoid the intersection of 75th Ave. and Lasalle Blvd. as the search got underway.