Some of the coronavirus testing kits sent to states and to at least 30 other countries have flaws and do not work properly, the Centers for Disease Control and Prevention said on Wednesday.

The kits were meant to enable states to conduct their own testing and get results faster than they would by shipping samples to the C.D.C. in Atlanta. But the failure of the kits means that states still have to depend on the C.D.C., which will mean several days’ delay in getting results.

The C.D.C. announced last week that it had begun shipping about 200 kits to laboratories in the United States and roughly 200 more to labs in more than 30 other countries. Each kit can test about 700 to 800 specimens from patients, the agency said.

  • What do you need to know? Start here.

    Updated Feb. 10, 2020

    • What is a Coronavirus?
      It is a novel virus named for the crown-like spikes that protrude from its surface. The coronavirus can infect both animals and people, and can cause a range of respiratory illnesses from the common cold to more dangerous conditions like Severe Acute Respiratory Syndrome, or SARS.
    • How contagious is the virus?
      According to preliminary research, it seems moderately infectious, similar to SARS, and is possibly transmitted through the air. Scientists have estimated that each infected person could spread it to somewhere between 1.5 and 3.5 people without effective containment measures.
    • How worried should I be?
      While the virus is a serious public health concern, the risk to most people outside China remains very low, and seasonal flu is a more immediate threat.
    • Who is working to contain the virus?
      World Health Organization officials have praised China’s aggressive response to the virus by closing transportation, schools and markets. This week, a team of experts from the W.H.O. arrived in Beijing to offer assistance.
    • What if I’m traveling?
      The United States and Australia are temporarily denying entry to noncitizens who recently traveled to China and several airlines have canceled flights.
    • How do I keep myself and others safe?
      Washing your hands frequently is the most important thing you can do, along with staying at home when you’re sick.

Officials have not said how many of the kits are flawed.

On trial runs in some states, the kits produced results that were “inconclusive,” Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, said at a news conference on Wednesday.

“Things may not always go as smoothly as we may like,” Dr. Messonnier said.

She said the C.D.C. was working closely with the states, and would send out new ingredients to laboratories that have encountered the problem.

There have been 13 confirmed cases of the infection in patients in the United States so far. About 850 evacuees have been quarantined at military bases after returning from China. Still others are under self-quarantine at their homes.

The flawed test kits are a separate issue from the mislabeled samples in San Diego that led officials to discharge from the hospital a woman who was sick from the coronavirus.

More than 1,100 people have died, nearly all of them in China, where there are more than 44,000 confirmed cases.