Three crew members are missing from a Gabon-registered tanker that caught fire on Monday in the South China Sea, a Malaysian maritime enforcement agency official said on Tuesday.

The Pablo, an Aframax-class crude oil tanker whose insurers are unknown, was traveling from China and was empty, according to ship-tracking data compiled by Bloomberg. The ship is designed to hold about 700,000 barrels of oil when full.

A vast shadow fleet of aging tankers has been enlisted to carry sanctioned oil across the globe, raising questions about safety and insurance standards. The Pablo was built in 1997, meaning it’s far beyond …