A sinkhole has opened up at a fertilizer plant in the US, causing about 980 million litres of radioactive water to leak into one of Florida's main underground sources of drinking water.

The sinkhole, which is about 14 metres in diameter, collapsed beneath a pile of waste material called a “gypsum stack”.

Sitting on top of the stack was a storage pond containing phosphogypsum, which is a radioactive by-product resulting from the production of phosphate.

Mosaic, the world's largest supplier of phosphate, said the hole at its New Wales facility in the town of Mulberry was discovered by a worker on August 27.

It said the sinkhole is believed to reach down to the Floridan aquifer, which supplies drinking water to millions of residents in the state. Aquifers are huge underground systems of porous rocks that hold water.