The Tokyo Electric Power Company (TEPCO) said in a statement that the water release restarted at 5:16 pm "with no abnormalities detected", after an hours-long halt.

In 2011, the Fukushima-Daiichi plant on Japan's northeastern coast went into meltdown after a huge earthquake and tsunami that killed 18,000 people. It was one of the worst nuclear disasters in history.

"At around 10:43 am (0143 GMT), electricity source line A stopped," Wednesday's TEPCO statement initially said without giving details.

The release of water treated through a filtration process called ALPS also stopped at the same time, it said.

The firm said the system to cool reactors remained operational and "no meaningful change" had been detected at plant facilities that monitor radioactivity.

TEPCO added that a worker had been injured during an excavation operation.

An inspection later found the worker was near an electric circuit when the incident occurred.

"Therefore, it is assumed that the worker damaged the cable during excavation work," the company said in a statement.

Earlier, a TEPCO spokesman told AFP that "there seems to be a link between this electricity loss and suspension of the ALPS operation."

"We are trying to figure out" a potential link between the injury and the electricity loss, he said.

The worker was conscious and not contaminated, but was seen by an on-site doctor and an ambulance was called.

Last year, Japan began releasing treated wastewater from the plant into the Pacific Ocean.

The facility was running out of space to build more water tanks, and TEPCO needed to clear the area for the much more hazardous task of removing radioactive fuel and rubble from three stricken reactors.

Japan argues that the water being released gradually over decades is harmless and heavily diluted with seawater.

The International Atomic Energy Agency (IAEA) and many leading economies have endorsed the release.

But China, later joined by Russia, banned all Japanese seafood imports, saying that Japan was polluting the environment.

IAEA officials and international experts are currently in Japan to review the water release.

Their mission to review "the safety and regulatory aspects of the discharge" is scheduled for April 23-26.