Anti-coronavirus controls that have shut down some of China’s biggest cities and fuelled public frustration are spreading as infections rise, hurting a weak economy and prompting warnings of possible global shockwaves.

Shanghai is easing rules that confined most of its 25 million people to their homes after complaints they had trouble getting food. But most of its businesses still are closed.

Access to Guangzhou, an industrial centre of 19 million people near Hong Kong, was suspended this week. Other cities are cutting off access or closing factories and schools.

Meanwhile, spring planting by Chinese farmers who feed 1.4 billion people might be disrupted, Nomura economists have warned. That could boost demand for imported wheat and other food, pushing up already high global prices.

The closures are an embarrassment to the ruling Communist Party and a setback for official efforts to shore up slumping growth in the world’s second-largest economy. They come during a sensitive year when President Xi Jinping is expected to try to break with tradition and award himself a third five-year term as leader.

Beijing has promised to reduce the human and economic cost of its “zero-Covid” strategy, but on Wednesday Mr Xi ruled out joining the United States and other governments that are dropping restrictions and trying to live with the virus.

“Prevention and control work cannot be relaxed,” he said, according to the official Xinhua News Agency. “Persistence is victory.”

The risk that China might tumble into recession is increasing, warned Ting Lu, Jing Wang and Harrison Zhang, of Nomura, in a report.

“The logistics crunch is worsening,” they said. “The markets should also be concerned about the delayed spring planting of grain in China.”

The government reported 29,411 new cases on Thursday, all but 3,020 with no symptoms. Shanghai accounted for 95% of that total, or 27,719 cases. All but 2,573 had no symptoms.

A health official warned on Wednesday that Shanghai did not have the virus under control despite its easing restrictions.

Some 6.6 million people were allowed to leave their homes in areas that had no new cases for at least a week. But at least 15 million others are still barred from going outdoors.

Most people have obeyed despite grumbling about shortages of food, medicine and access to elderly relatives who need help. But videos on the popular Sina Weibo social media service show some trading punches with police.

Grape Chen, a data analyst in Shanghai, said she was worried about getting medicines for her father, who is recovering from a stroke. She called police after getting no response from an official hotline but was told quarantine rules bar officers from helping.

“We are willing to co-operate with the country,” Ms Chen said. “But we also hope that our lives can be respected.”

The city government of Suzhou, a centre for smartphone manufacturing and other high-tech industry west of Shanghai, told its 18 million people to stay home when possible.

Taiyuan, a blue-collar city of four million in central China, suspended inter-city bus services, according to the official China News Service. Ningde in the south-east barred residents from leaving.

All but 13 of China’s 100 biggest cities by economic output are under some form of restrictions, according to Gavekal Dragonomics, a research firm.

“The intensity is increasing,” it said in a report this week.

The volume of cargo handled by the Shanghai port, the world’s busiest, has fallen 40%, according to an estimate by the European Union Chamber of Commerce in China. Carmakers have suspended production due to the disruption in deliveries of supplies.

Restrictions on areas that produce the world’s smartphones, consumer electronics and other goods are prompting forecasters to cut expectations for this year’s economic growth to as low as 5%, down sharply from last year’s 8.1% expansion.