One person died and another two were unaccounted for after a pleasure boat capsized in the San Francisco Bay on Tuesday afternoon, fire officials said.

Sixteen people were rescued, three of whom had injuries severe enough to require hospitalization, said Lt. Mariano Elias of the San Francisco Fire Department. A dog that had also been aboard the pontoon boat died, he said.

Fire officials initially said that they had been responding to a boat fire that had been called in just after 3:30 p.m. on Tuesday. When they arrived, they found the boat sinking but no evidence of a fire, they said.

In total, there were 19 people onboard, the San Francisco fire chief, Dean Crispen, said at a news conference. Three of them were being treated for what appeared to be impact injuries from hitting the water, he said. Rescue workers were continuing to search for the two remaining passengers using helicopters and scuba divers, he said.

“We are going to continue for hours to make sure we find these two missing people, if possible,” Chief Crispen said.

One passenger was “severely injured” and needed cardiopulmonary resuscitation, so rescue workers immediately brought the patient to the shore, he said. But the person died of their injuries, he said.

The boat, which had stalled about 600 yards from Alcatraz Island, has since sunk and is 120 feet below the surface, he said.

Chief Crispen said that he had spoken to some of the survivors, who were “incredibly upset.” He said that the three-level boat was already mostly submerged when rescue workers arrived.

“Some people were in the water. Some people were on the boat. Some people were just falling into the water,” he said.

Lieutenant Elias said he did not know whether the boat had been headed to or from Alcatraz, a tourist destination best known for its shuttered prison. He said there were 11 boats from multiple fire departments on the water helping with the operation.

“This is an all-hands-on-deck search, and hopefully, rescue,” Mayor Daniel Lurie of San Francisco said at the news conference with Chief Crispen.

This is a developing story. Check back for updates.