A pleasure-boat outing on San Francisco Bay ended in tragedy on Tuesday when a large pontoon boat capsized near Alcatraz Island, killing one person and sending emergency crews into an hours-long search for two people still missing.

What happened

The vessel, a three-deck pontoon boat with 19 people aboard, went over in the water about 600 yards from Alcatraz at around 3:35 p.m., authorities said. The incident was first reported as a boat fire, but officials said they found no evidence of flames; the boat appears to have capsized. When firefighters reached the scene, part of the vessel was already submerged.

The toll

One person was brought ashore with severe injuries and, despite CPR, was pronounced dead, officials said. Sixteen people were rescued from the water, 13 brought to shore and three taken to a hospital, while two remained missing as of Tuesday evening. With one dead, 16 rescued and two unaccounted for, the count matched the 19 reported aboard.

The search

The San Francisco Fire Department said it was in "full rescue mode," with about 11 boats plus divers searching the bay alongside the U.S. Coast Guard and other agencies. The waters around Alcatraz are cold and the currents strong, conditions that raise the urgency of any water rescue and can carry a person far from where they went in.

What comes next

The cause of the capsizing was not immediately clear, and officials had not released the names of the dead or missing. This is a developing story; the figures here reflect what authorities had confirmed as of Tuesday evening and may change as the search continues.