One person has died, and three others are missing after a pontoon boat capsized around 600 yards from Alcatraz Island on Tuesday.

A report of a vessel in distress came in at 15:37 local time (22:37 GMT), San Francisco Fire Department chief Dean Crispen said.

A marine unit first on the scene witnessed a man in the water "in severe distress" and initiated CPR, Crispen said. He was declared deceased when brought to shore.

He said 20 adults, mostly family members, were on the three-deck pontoon boat, a 50ft (15m) cabin cruiser called Volare, and they were "engaging in some kind of memorial service".

Authorities said a search and rescue operation by the San Francisco Fire Department and the US Coast Guard would continue throughout the evening.

Three people on the boat were injured and taken to a local hospital, where they were in a stable condition, Crispen told a news conference.

The man who died was 79-year-old Clifford Joseph Boisa, said the San Francisco medical examiner's office.

Boisa was a resident of Sutter County, which is around a two-hour drive north-west of San Francisco.

The other 13 members on the boat returned safely to shore and were not injured.

The fire department chief said the initial alert had indicated a vessel was on fire.

But he said later there was no evidence of a blaze when the fire service arrived at the scene, with witnesses reporting rough seas and a vessel that began to take on water and was turned over in the bay.

Longshoreman Justin Marceline, who, alongside fisherman Mike Montoya, helped rescue people from the vessel, according to Reuters, said it was "complete chaos when we showed up".

"Every time we had to grab a person, each one of them, either they were exhausted, or they were frantic and were flailing," Marceline said.