BEIJING (AP) — China’s exports rose 15.7% over a year ago in March while imports were flat amid disruptions due to coronavirus outbreaks as the ruling Communist Party enforces a “zero-COVID” strategy to isolate every case.

Exports rose to $276.1 billion despite anti-virus controls in Shanghai and other industrial hubs that are causing factories to reduce production, customs data showed Wednesday. Imports rose less than 1% to $228.7 billion.

China’s infection numbers are relatively low, but the “zero-COVID” strategy has confined most of Shanghai’s 25 million people to their homes since late March and suspended access to other manufacturing regions.

The anti-virus curbs are adding to concerns over global trade disruptions that persist from the pandemic. Chinese officials say they are taking steps to keep ports functioning, but automakers and other factories have cut production due to problems with supplies.

Local outbreaks have “caused great pressure on production and operation of some enterprises and the stability of the supply chain,” said a customs official, Li Kuiwen, at a news conference. Li said the customs agency “makes every effort to coordinate ports well.”

An economic slowdown triggered by an official campaign to cut debt in China’s vast real estate industry, meanwhile, has sapped consumer demand. Economic growth slid to 4% over a year earlier in the final quarter of 2021, down from the full year’s 8.1%.

Exports to the United States rose 22.4% over a year earlier to $47.3 billion in March despite lingering tariff hikes in a feud over Beijing’s technology ambitions. Imports of American goods rose 11.5% to $15.2 billion.

That meant the politically volatile trade surplus with the United States widened by half over a year earlier to $32.1 billion. That imbalance was one of the factors that prompted then-President Donald Trump to hike tariffs on Chinese goods in 2019.

With almost no growth in imports, China’s global trade surplus more than doubled to $47.4 billion.

Imports from Russia, a major gas supplier, fell 26.4% from a year earlier to $7.8 billion. Exports to Russia edged down 7.7% to $3.8 billion.

Beijing has criticized trade and financial sanctions imposed on Moscow by the United States, Europe and Japan over its invasion of Ukraine. But Chinese companies appear to be abiding by them while trying to guard against possible losses in dealings with Russia.

Trade and manufacturing appear likely to suffer a bigger impact this month due to the shutdown of most businesses in Shanghai and suspension of access to Guangzhou, a manufacturing and trade center in the south, and to industrial centers of Changchun and Jilin in the northeast.

Managers of the port of Shanghai, the world’s busiest, say its operations are normal. But the European Union Chamber of Commerce in China has said its member companies estimate the volume of cargo handled by the port every day is down 40%.

Exports to the 27-nation European Union fell 9.1% from a year ago to $44.4 billion while imports tumbled 41.6% to $24.3 billion. China’s surplus with Europe jumped 179.3% to $20.1 billion.