Officials across the country are racing to provide coronavirus tests to diagnose infections and to identify recovered patients with antibodies that may help others battle COVID-19, the disease it causes.

But some COVID-19 antibody tests, including those being used by public health departments in Denver and Los Angeles and provided to urgent care centers in Maryland and North Carolina, were supplied by Chinese manufacturers that are not approved by China's Center for Medical Device Evaluation, a unit of the National Medical Product Administration, or NMPA, the country's equivalent of the U.S. Food and Drug Administration, NBC News has found.

Two U.S. companies — Premier Biotech of Minneapolis and Aytu Bioscience of Colorado — have been distributing the tests from unapproved Chinese manufacturers, according to health officials, FDA filings and a spokesman for one of the Chinese manufacturers. Many of the unapproved tests appear to have been shipped to the U.S. after the FDA relaxed its guidelines for tests in mid-March and before the Chinese government banned their export just over two weeks later.

If COVID-19 antibody tests are unreliable, they can produce false results, either negative or positive, health officials said. The use of such tests has been widely discussed as a way to ensure that employees are healthy enough to go back to work and to find COVID-19 survivors who may be able to provide blood plasma to severely ill patients.

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Officials at the Association of Public Health Laboratories have expressed concern about the reliability of the numerous antibody tests being sold or used across the country with little scrutiny. Scott Becker, the association's chief executive, told NBC News that FDA officials are working with the Centers for Disease Control and Prevention, the National Institutes of Health and the Biomedical Advanced Research and Development Authority to evaluate the performance of the tests.

In the meantime, Becker said, any U.S. companies that are selling tests to public health agencies should push to have the FDA evaluate them in the multi-agency study.

Not on the list

The FDA moved to accelerate and expand the availability of COVID-19 diagnostic tests after coming under criticism for the slow pace of test approval in the U.S.

On March 16, after the Department of Health and Human Services said the pandemic justified the authorization of emergency use of diagnostics for detection and diagnosis, the FDA relaxed its policies, allowing tests to be sold even if it had not approved them.

In China, the NMPA has been reviewing COVID-19 test kits since January to ensure that they "meet the requirements of 'safety, effectiveness and quality control,'" according to the NMPA website. A U.S. expert said the Chinese agency is considered "rigorous" and "demanding" in its oversight of products.

On April 2, the NMPA published its most recent list of approved COVID-19 test manufacturers after a March 31 announcement from China's Commerce Ministry restricted the export of medical materials. The ministry said its restrictions aimed "to strictly control quality, maintain export order, and crack down on counterfeit and shoddy products."

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Tests made by two Chinese manufacturers, Hangzhou Biotest Biotech Co. and Zhejiang Orient Gene Biotech, are not on the approved list, but they are being sold in the U.S.

There is no indication that either test is unreliable.

Hangzhou Biotest Biotech, for example, provides U.S.-based Premier Biotech's COVID-19 tests, according to the FDA website. Premier supplied tests to the Los Angeles County Public Health Department, which teamed up with the University of Southern California for a comprehensive antibody testing study that began this month. County officials hope the study will show how deadly the coronavirus is and demonstrate the effectiveness of strategies like social distancing and wearing masks.

Julie Labich, a spokeswoman for USC's Sol Price School of Public Policy, did not provide a comment when asked about the Premier test's lack of approval by the NMPA. A spokesman for Los Angeles County did not respond to a request for comment.

Zhejiang Orient Gene Biotech supplies U.S.-based Aytu Bioscience with a COVID-19 test that has not been approved, according to Bryan Fang, a spokesman for Healgen Scientific, the U.S. subsidiary of Zhejiang Orient in Houston.

Josh Disbrow, chief executive of Aytu, confirmed by phone that Zhejiang Orient's tests have not been approved by the NMPA. He emphasized that the tests have been validated in a study by third-party clinical researchers.

While that study showed a satisfactory performance of the test, the researchers said that their findings were limited and that results for the Zhejiang Orient tests needed to be compared with results from other antibody tests to gauge performance.

Asked whether Aytu notifies its customers that its test has not been approved by Chinese authorities, Disbrow said the company made no such statements. "It is not something that has come up," he said. "The idea of approval is changing by the day."

NBC News telephoned Premier to discuss its importation of unapproved COVID-19 tests from the second Chinese firm, Hangzhou Biotest Biotech. Jess Perlman, an employee answering the phone at Premier, declined to identify the manufacturer of its tests, saying it is against Premier's policy to do so.

After publication of this article, a lawyer for Premier contacted NBC News to stress that the tests were lawfully exported from China and are “lawfully on the U.S. market under FDA’s COVID-19 policy.” The lawyer also said that the “diagnostic has been validated by testing as per FDA’s policy.”

Labich of USC also sent a post-publication statement saying the tests were legally exported and legal for sale in the U.S., and that they had been found to be accurate. Labich said that Premier reports the accuracy of the tests to the FDA, and that two separate assessments found the tests’ negative readings for coronavirus antibodies were correct 99.5 and 100 percent of the time.

“These data show that the tests have enough accuracy to be used for public health surveillance purposes,” Labich said.

Responding to an email requesting information about the antibody test it has supplied to Premier, Hangzhou said via an automated response Wednesday, "We are sorry to inform you, according to the latest regulatory policy requirements from government, we suspended the export sales of the COVID-19 IgG/IgM Rapid Test."

In early April, Aytu Bioscience supplied tests to the Denver Public Safety Department, according to a company news release and Kelli Christensen, a spokeswoman for the Public Safety Department, which oversees the city's first responders.

In a phone call Monday, Christensen said that the Aytu tests had been in use as a screening tool for a week and that she had heard anecdotally that they were generating a considerable number of false positives early on.

"There have been more presumptive positives than confirmed cases," Christensen said.

In an email exchange, Fang of Healgen said its parent, Zhejiang Orient, applied in early April for approval for its test from China's Center for Medical Device Evaluation and is still waiting. Because the Chinese government banned manufacturers from exporting COVID-19 test kits after April 1 if they are unapproved, Fang said, Zhejiang Orient stopped exporting the tests and told its clients that it did not have the necessary license.

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Export records show that on April 10, Healgen received two shipments from Zhejiang Orient in China. COVID-19 test kits were in those shipments, Fang said, because they had been shipped before the April 1 ban.

On Wednesday, Aytu published a news release announcing that it had placed an order for 1 million test kits from an unidentified manufacturer. Disbrow, Aytu's chief executive, said in the release that another order for 500,000 tests was "awaiting customs clearance."

Although the FDA has relaxed rules for COVID-19 tests, it does require manufacturers to validate the tests before use and to notify customers if the tests have not yet been reviewed by the FDA. The agency also says test results should not be used as the sole basis to diagnose or inform a person's infection status.

The FDA said it will perform "preliminary reviews" to identify problems with the validation tests submitted to it by the manufacturers. If it identifies a problem, the FDA said, it will work with manufacturers to address it. Manufacturers whose tests have problems that cannot be resolved quickly will be expected to pull the tests from the market, the FDA said.

Aytu's website follows the FDA protocol, noting that the agency has not reviewed its tests. Premier did not immediately respond to a request for comment.