Beijing, China - China said on Friday it would impose "special port fees" on ships operated by and built in the US after Washington announced charges for Chinese-linked ships in April.

Incremental fees on American ships will be collected at Chinese ports from October 14, Beijing's transport ministry said in a statement.

The US shipbuilding industry was dominant after World War II but has gradually declined and now accounts for just 0.1% of global output.

The sector is now dominated by Asia, with China building nearly half of all ships launched, ahead of South Korea and Japan.

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US Trade Representative Jamieson Greer said in April new port fees on Chinese ships would help reverse Beijing's dominance and "send a demand signal for US-built ships."

A Chinese transport ministry spokesperson called the actions "protectionist" as Beijing announced its port fees on Friday.

US ships arriving in China will be charged 400 yuan ($56) per net tonne. That fee will go up to 640 yuan in April and then increase annually.

The charges apply to US-flagged vessels and ships built in the US, as well as those owned or operated by American firms or individuals.

Each ship is charged at its first port of call – not at each place it docks – and a vessel will be charged no more than five times a year, the ministry said.

The charges take effect the same day US ports begin applying fees for Chinese-built and operated ships arriving there.

That move stemmed from a probe into China's shipbuilding sector launched under the previous US administration.

There will be separate fees for Chinese-operated ships and Chinese-built ships, and both will gradually increase over subsequent years.

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For Chinese-built ships, the fee starts at $18 per net tonne or $120 per container – meaning a ship with 15,000 containers could see a whopping fee of $1.8 million.

The Chinese spokesperson called Beijing's levies a "legitimate measure to safeguard the lawful rights and interests of Chinese shipping companies."

"We urge the US side to immediately correct its wrongful practices and cease its unwarranted suppression of China's shipping industry," the unidentified spokesperson said.