A remote control robot has uncovered a stream of highly radioactive water in the building housing a reactor at Japan's crippled Fukushima Daiichi nuclear plant.

The leak is possibly from the battered reactor core, Tokyo Electric Power Company said this morning.

Video released by Tepco shows a stream of water flowing across the floor and into the building's basement from the reactor, one of the reactors that melted down in the aftermath of Japan's 2011 earthquake and tsunami.

The water was found to have high levels of radioactive caesium and cobalt at 24,000 becquerels per litre according to Tepco.

These levels are far higher than what is allowed to be dumped into the ocean.

Tepco says none of this water has leaked out of the building itself.

Tepco and Japanese media have said that there is a chance that the water is flowing from holes in the reactor itself, which contains melted fuel rods.

The company has said that it does not know how much water has leaked out or when the leak began.