The operator of a damaged nuclear power station in north-eastern Japan said on Tuesday a partial fuel meltdown was believed to have taken place at two more reactors at the plant.

The latest update suggested that three of the six reactors at the Fukushima Daiichi nuclear plant were believed to have suffered fuel meltdowns after the March 11 earthquake and tsunami crippled the plant.

The plant has leaked radioactive substances into the environment ever since.

The operator, Tokyo Electric Power Co (TEPCO), said earlier that a meltdown was believed to have occurred at reactor 1 soon after the disaster knocked out the plant’s cooling systems with most of its fuel having melted down to the bottom of the pressure vessel.