Radiation readings at a drainage channel at Japan's crippled Fukushima nuclear power station doubled in the span of 24 hours, the plant's operator said Thursday.

Water samples taken Wednesday from the ditch, located near a storage tank that leaked 300 tons of radioactive water in August, had beta radiation levels of 140,000 becquerels per liter, up from 59,000 becquerels per liter the day before, Tokyo Electric Power Co. said.

TEPCO said the increase may have been due to highly radioactive dirt flowing into the ditch as a result of recent heavy rains.

The ditch is located near a group of tanks used to store water that becomes severely contaminated after being used to cool the plant's reactors.

That water must be pumped in because three of Fukushima's reactors lost their cooling systems and suffered partial meltdowns in the devastating 2011 earthquake and tsunami.

TEPCO is also working against the clock to contain the large amount of rainwater expected to fall at the plant with the arrival of Typhoon Francisco, which is projected to hit northeastern Japan on Oct. 27.

To prevent rainwater from overflowing leak-protection barriers surrounding the tanks, as occurred with last week's Typhoon Wipha, TEPCO has begun transferring the water from that previous storm into underground pools.

The water being pumped out contains a maximum of 970 becquerels of radiation per liter of strontium-90, more than 30 times the regulatory limit for release into the sea outside the plant.

Thus far, TEPCO has tried to pump rainwater into water-treatment tanks.

But those tanks are already full and the company says that, with another typhoon on the way, it has no other choice but to use three underground pools where leaks have previously occurred. EFE