China has defended its decision to suspend imports of Japanese seafood in response to the release of treated and diluted water from the Fukushima Daiichi nuclear power plant into the ocean.

Japanese Prime Minister Kishida Fumio called on Chinese President Xi Jinping to lift the measure during a bilateral summit on Thursday in San Francisco.

On Friday, Chinese Foreign Ministry spokesperson Mao Ning said it is "just, reasonable and necessary" for countries to take appropriate precautions to safeguard food safety and people's health.

Water used to cool molten fuel at the plant mixes with rain and groundwater. The accumulated water is treated to remove most radioactive substances, but tritium remains.

The plant's operator dilutes the water to reduce tritium levels to about one-seventh of the World Health Organization's guidelines for drinking water, before releasing it into the ocean.

Mao described the water as "nuclear-contaminated." But she also said that China hopes to find an appropriate solution through "discussions and negotiations."

She also said Xi and Kishida reaffirmed the need to promote mutually beneficial strategic relations.

The Japanese leader stressed the importance of peace and stability in the Taiwan Strait during their talks.

In response, Mao said Beijing will not allow any interference in China's internal affairs. She also stressed that the "one-China principle" is fundamental to cross-strait peace and stability.