The fire in Basin A was first reported around 8:30 p.m., according to the Los Angeles County Fire Department. Firefighters responded and poured water on the 100-foot vessel from the dock at the end of Bora Bora Way.
Witness video captured the sounds of several explosions as firefighters battled the flames.
Luxury yacht docked at Marina del Rey sinks after fire
But the interior flames appeared to resist the water hoses and the boat continued sustaining damage. It quickly began taking on water from the hoses as the flames, possibly fueled by a gas source, continued to burn.
The yacht began listing, and by around 10:30 p.m. firefighters were ordered to evacuate the dock. The boat began slowly overturning onto its side and sinking into the water.
There were no major injuries reported. Two people on board exited safely, though one reported a minor cut to the arm.
There was no word on how the fire started. Authorities said it's possible ammunition was on board the vessel.
The boat is named The Admiral, but the identity of the owner was not immediately available.