A partial power outage at the crippled Fukushima Daiichi nuclear power plant on Wednesday morning stopped the release of treated and diluted water into the ocean.
The plant's operator, Tokyo Electric Power Company, says the cooling of nuclear debris has been maintained.
TEPCO said one of the systems that supply electricity to the plant stopped at around 10:43 a.m.
The utility said the loss of power led to automatic stoppage of discharging treated and diluted water into the ocean. The fifth round of discharges started on Friday.
TEPCO says the safety of critical areas of the plant has been ensured by sourcing power from other lines. This includes cooling of spent nuclear fuel and debris in damaged reactors.
The operator also says radioactive levels around the facility have showed no abnormal figures.
TEPCO is investigating what caused the disruption to the power supply.
The plant suffered a triple meltdown in the 2011 earthquake and tsunami.
Water used to cool molten fuel has been mixing with rain and groundwater seeping into the damaged reactor buildings. The accumulated water is being treated to remove most radioactive substances, but still contains tritium. The treated water is being stored in tanks at the plant.
Before releasing the treated water into the ocean, the utility dilutes it to reduce the tritium levels to about one-seventh of the World Health Organization's guidance level for drinking water.
Meanwhile, a worker was reportedly injured while engaged in drilling work outside a building inside the plant compound at around 10:47 a.m. TEPCO reportedly called an ambulance to rush the person to hospital. The person reportedly remains conscious.
TEPCO is checking whether the accident is related to the power outage or not.