One person was missing and 17 people were rescued after a fire broke out on a pontoon near San Francisco’s Alcatraz Island on Tuesday, authorities said.

The US coast guard confirmed search-and-rescue efforts were “ongoing” Tuesday afternoon.

KTVU Fox 2 captured a video of a red boat partially submerged in the water. Several people were reportedly receiving medical attention, but the extent of any injuries remained unclear.

The vessel, described as a “pontoon pleasure boat” by San Francisco fire Lt Mariano Elias, was about 600 yards (548 meters) from the island when the fire began.

Spokespeople for the San Francisco fire department and the Oakland police department did not immediately respond to an inquiry about the origins of the blaze and whether there were fatalities.

Millions of visitors descend upon Alcatraz Island every year to see the eponymous, now-shuttered prison where some of the nation’s most infamous criminals were once incarcerated.

More details soon …