Amazon, as well as vendors on its platform, began limiting the number of tests per person Wednesday.

National pharmaceutical chains CVS and Walgreens announced a maximum limit of six and four kits, respectively, per customer.

For Walgreens, the decision came after an “incredible demand for at-home rapid testing” strained the company’s inventory, according to a press release.

The company added that it plans to “work diligently” with its suppliers to get more tests on its shelves, although it anticipates some stores may experience a temporary shortage.

“We ask that our customers please show patience and understanding as together, we continue to navigate the evolving pandemic environment,” said Walgreen President John Standley in the statement.

With a shortage of rapid at-home tests, Americans are lining up across the country — sometimes waiting for hours — to get a test at a clinic or mobile testing site.

In the capital Washington, one centre said that the number of tests it performs daily had quadrupled over the past two weeks.

According to health authorities, the fast-spreading Omicron variant is now the main coronavirus strain in the US, accounting for 73.2% of new cases over the week ending Dec 18.

On Tuesday President Joe Biden announced the purchase of 500 million rapid tests by the federal government. However, the additional tests are not expected to be available until January.