Emergency crews are keeping an eye on the scene amid concerns that the blaze could spread to other tanks in the area, including a seven million litre ethanol tank.

The Port Kembla Port Corporation said a large ethanol tank, several storeys high, exploded onshore outside the port boundary near jetty six, with flames shooting about 100m into the air.

The Australian Workers Union said it would launch an investigation into the cause of the explosion.

A 56-year-old man, a worker with ethanol producer, Manildra Group, which owns the tank, was taken to Wollongong Hospital with minor burns and injuries and was in a stable condition, an ambulance spokeswoman said. One man previously thought to be missing has been accounted for.

So far there is no word on what triggered the explosion.