Six workers at Japan's crippled Fukushima nuclear plant have been doused with highly radioactive water after wrongly disconnecting a pipe.

The accident sent toxic water spilling on to them and the entire floor of the facility which houses a set of three units designed for water treatment.

The workers were wearing face masks with filters, protective hazmat suits and raingear, and their exposure is believed minor but still under investigation, said Yoshimi Hitosugi, spokesman for operator Tokyo Electric Power Co (Tepco).

The workers were part of an 11-member team, and the remaining five were not splashed, he said. They managed to reattach the pipe later.

The accident is latest in a string of mishaps. A week earlier, workers overfilled a storage tank without fully checking water levels, and caused a leak of 430 litres (113 gallons) of contaminated water which is thought to have run into the sea.

Tepco has been battling to contain radioactive water since the plant suffered triple meltdowns and hydrogen explosions following a devastating earthquake and tsunami in March 2011.

In the latest incident, the company said a worker mistakenly detached a pipe connected to a treatment system which removes salt from the hundreds of tonnes of cooling water Tepco pumps over the melted fuel in wrecked reactors.

Tepco said seven tonnes of water were spilled in Wednesday's incident but was contained within the site.

Masayuki Ono, Tepco's general manager, said: "At the moment we only have provisional figures, but we think the amount of water that leaked was about seven tonnes.

"We have confirmed the leak has stopped within the building and has not seeped out into the wider area."

The accidents at the Fukushima Daiichi plant, 130 miles (220 kilometres) north of Tokyo, are adding to a crisis no one seems to know how to contain, and stirring doubt over Tepco's abilities to carry out a complex cleanup widely expected to take decades.