Japan's stricken Fukushima nuclear power plant has leaked more than 600 litres of water over the weekend. Engineers have had to briefly suspend cooling operations at a spent-fuel pond.

The operator, Tokyo Electric Power Corporation, reports two main leakages on its website.

One was from a pump near the plant's office building, and another was from a back-up cooling system at reactor number 4. It's believed the leaks are caused by freezing, due to the cold weather.

Tepco says the water includes radioactively contaminated water that has been purified. But they are examining whether or not the water has flowed into the ocean.