TOKYO, April 13 (CNA) - The Japanese government plans to release more than 1 million tonnes of contaminated water from the destroyed Fukushima nuclear plant into the ocean, Prime Minister Yoshihide Suga said on Tuesday (Apr 13), in a controversial decision that follows years of debate.

Work to release the water will begin in about two years and could take decades to complete, but has already sparked fierce opposition from local fishing communities, anti-nuclear activists and neighbours Beijing and Seoul.

The government argues that the release will be safe because the water has been processed to remove almost all radioactive elements and will be diluted.

It has support from the International Atomic Energy Agency (IAEA), which says the release is similar to processes for disposing of waste water from nuclear plants elsewhere in the world.

Japan's Prime Minister Yoshihide Suga told a ministerial meeting that disposing of the water was an "inevitable task" in the decades-long process of decommissioning the nuclear plant.

He said the release would happen only "after ensuring the safety levels of the water" and alongside measures to "prevent reputational damage".

Around 1.25 million tonnes of water has accumulated at the site of the nuclear plant, which was crippled after going into meltdown following a tsunami in 2011.

It includes water used to cool the plant, as well as rain and groundwater that seeps in daily.

An extensive pumping and filtration system known as ALPS (Advanced Liquid Processing System) extracts tonnes of newly contaminated water each day and filters out most radioactive elements.

But local fishing communities fear releasing the water will undermine years of work to restore confidence in seafood from the region.

"They told us that they wouldn't release the water into the sea without the support of fishermen," Kanji Tachiya, who heads a local fisheries cooperative in Fukushima, told NHK ahead of the announcement.

"We can't back this move to break that promise and release the water into the sea unilaterally."

The decision also prompted regional opposition even before it was official, with South Korea's foreign minister on Monday expressing "serious regret over this decision, which could have a direct or indirect impact on the safety of our people and the surrounding environment in the future".

Chinese foreign ministry spokesman Zhao Lijian urged Japan to "act in a responsible manner" over the discharge of the water.

"To safeguard international public interests and Chinese people's health and safety, China has expressed grave concern to the Japanese side through the diplomatic channel," Zhao said Monday.