HONG KONG — One man made fake Honeywell N95 respirators at a makeshift factory on a farm. Pharmacies sold ineffective knockoffs of a Chinese version of Clorox. In one Chinese province, authorities seized more than seven million masks that were substandard, mislabeled or counterfeited.

China’s vast manufacturing machine has moved into overdrive to supply the country and the world with masks, testing kits, respirators and other gear to fight the global coronavirus pandemic. Companies big and small that once manufactured other items are now in the business of making anti-coronavirus gear — and regulators in China are struggling to enforce standards while encouraging the flow.

Those tensions blew into the open internationally this week. Officials in Spain said testing kits it bought from a Chinese company had only a 30 percent accuracy rate, rather than the 80 percent rate they had expected.

The Chinese embassy in Spain  the company that made the test kits, Shenzhen Bioeasy Biotechnology, had not been on Beijing’s list of certified providers nor a supplier to aid packages organized by Chinese companies like Alibaba, the e-commerce giant. Market regulators in Shenzhen, the southern Chinese city where the company is based, said they were investigating the matter.

Spanin bought the tests from an unnamed third-party distributor but argued that they did not need to wait for a certified list from China, saying they had already received European certification. “Spain follows the norm of the European Union,” the health ministry said.

Still, the news was unwelcome for Spaniards who have waited for several days for their government’s promised rollout of hundreds of thousands of tests to help track the spread of the virus. The spat came a day after the Spanish government announced a $475 million order for emergency medical equipment from China.

In a statement on social media, Bioeasy said that Spanish officials did not understand how to conduct the test and that it made videos and issued instructions to help them.d has bec

It expanded its capacity significantly after the coronavirus first emerged in the city of Wuhan, as factories retooled or expanded and new companies sprang up. BYD, a company that normally makes electric cars, says it could make five million masks and 300,000 bottles of disinfectants a day. Foxconn, a Taiwanese company that typically makes gadgets like iPhones on behalf of Apple and other companies in giant Chinese factories, churned out 10 million masks for its own employees in February and said it was close to making two million a day.

With its own outbreak seemingly tamed for now, China has looked to sell or donate masks and other gear, in part to improve its public image after it tried, disastrously, to play down its coronavirus crisis in January. Chinese-made masks have been part of aid packages to Europe, to developing countries and to the United States. In a tweet on Thursday, Gov. Andrew M. Cuomo of New York thanked Huawei, the Chinese telecommunications company that has been mostly banned from doing business in the United States over Washington’s security concerns, for donations of masks and other protective gear.

But even as it encourages production, the Chinese government has also had to step up enforcement efforts to stop defective and uncertified products. That presents a challenge to Chinese officials, who have to ensure quality standards are met even as they push factories to make what the world needs.

 But the sheer size of China’s response and the lingering effects of its own coronavirus containment efforts have complicated the process.

“Every time when something major happens in society like this virus outbreak, there is a lot of demand and different kinds of companies try to get in,” said Cody Zhang, the chief executive officer of a start-up seeking certification for its own products, including a disinfecting robot. “It becomes hard at the beginning to figure out which ones are good and which ones are bad.”

Regulators have shut down tens of thousands of shops making fake masks, faulty thermal temperature guns and disinfectants that don’t work, according to government disclosures. Thousands of companies and individuals have been punished for offenses like making counterfeits or price gouging, according to China’s State Administration for Market Regulation, which oversees standards and testing.

Earlier this month, Chinese regulators vowed to step up cooperation with local law enforcement to stamp out counterfeits and shoddy goods. “In our next steps, we will continue to take solid action toward a ‘severe punishment and no amnesty’ approach,” said Chen Zhijiang, an official with the market regulation agency. The agency did not respond to a request for comment.

Police have been sent out to raid the operations of counterfeiters across China. In the city of Chongqing, some 88,500 officers filed hundreds of cases. Many of those were related to poor quality protective gear. Others included the manufacturing of counterfeit drugs and medical devices.

At the same time, local officials have worked to streamline the certification process to bring new capacity and new devices online.

Mr. Zhang, whose robot start-up in Shenzhen is called YouIbot, and his engineers built an antivirus robot over a frenzied two weeks. As it rolls along the floor, six ultraviolet light bars sanitize the surface, and its infrared camera can scan patients and other people in public for fevers.

Shenzhen officials jumped in to help get the robot certified, Mr. Zhang said. Companies making “epidemic prevention” products are placed in a priority line for regulatory approval. In mid-March, a senior city official made a high-profile visit to the offices of YouIbot and other start-ups with ambitions to make outbreak-related products, and spoke to city cleaners in a media campaign to emphasize how the city is getting back to work.

The effort helped shorten YouIBot’s ability to deliver a robot to one month from three for the subway system in the adjacent city of Guangzhou, said Keyman Guan, YouIbot’s marketing director.

“It happened in just a blink,” Mr. Guan said.

Companies looking to get into outbreak prevention can readily find money. Starting up can prove to be harder.

In Hong Kong, a semiautonomous Chinese city, long lines formed outside pharmacies as desperate residents sought masks. Seeing an opportunity, Tong Ka-fai, a filmmaker and former child actor, raised money from his production company’s investors and from his film editor to buy a mask-making machine in Chennai, India. In interviews, he said he had enough raw material to make 10 million masks in two or three months.

“I am not the first to see this market. I may even be one of the last ones,” he said in an interview in February. “But I took action right away.”

Mask Factory, his new mask-making company, offered a subscription plan that promised to send customers a box of masks every month.

“I wanted to avoid the desperate feeling of hunting for masks every time I ran out,” said Scarlett Chan, a secondary school teacher, who subscribed. “The plan promised one box every month. It sounded too good.”.

“I feel really stupid,” Ms. Chan said. “I wanted to support a local venture but am now one of the people who fell into a trap.”

Mr. Tong said the company had been hacked, snarling its operations, but that refund requests had been processed and new products would be shipped.

“Our haters and competitors keep exaggerating what we haven’t done well,” he said, “but our supporters really believe in us.”

Cao Li contributed reporting from Hong Kong, and Raphael Minder from Madrid.