Medical take a patient's coronavirus test during a trial run for a new FEMA drive-thru coronavirus testing clinic at CVS at 720 Boston Turnpike in Shrewsbury, MA on March 19, 2020.

CVS Health has opened its first drive-thru testing location for the coronavirus, in Massachusetts.

Starting around 3 p.m. on Thursday, the health-care company began offering tests in a pharmacy parking lot in Shrewsbury, about 50 miles west of Boston in Worcester County. It is not open to the general public. Tests at the site are limited to first responders, such as firefighters, nurses and police, who are referred by state and public health officials, spokesman Joe Goode said. He said the company is not charging for the tests.

CVS is one of four retailers that pledged on March 13 at a White House press conference that it would open drive-thru testing locations to help detect COVID-19 and fight its spread.

Walmart, Target and Walgreens also committed to hosting drive-thru testing in their parking lots. The other retailers have not yet announced the timing or locations of tests.

Access to testing in the U.S. hasn't kept up with rising demand. Earlier in March, the Centers for Disease Control and Prevention said tests were available in all 50 states and more test kits were coming soon. A few days later, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told a committee of Congress members that the nation wasn't processing as many coronavirus tests as other countries and called it "a failing."

That criticism and growing frustration prompted the Trump administration to enlist the help of the private sector, including many of the nation's top retailers and health-care companies, on March 13. At a press conference in the Rose Garden, CEOs of Walmart, Target and other companies took turns at the microphone and promised to help boost testing.

"Normally, you would view us as competitors, but today we're focused on a common competitor and that's defeating the spread of the coronavirus," Target CEO Brian Cornell said. "We look forward to working with the administration to do our fair share to alleviate this growing threat."

Politicians, including New York City Mayor Bill de Blasio, have also criticized the uneven way tests have been distributed, saying they've been available to celebrities and athletes even as sick members of the public struggle to find them. For example, after a Brooklyn Nets player tested positive for COVID-19, the entire team was tested — even players that did not have any symptoms.

CVS spokesman Joe Goode said the company tried to open its first testing site as quickly as possible.

"This is our first experience endeavoring this type of testing outside of one of our store locations," he said. "There were a lot of operational challenges. We wanted to make sure that we staged this testing site properly. We worked with local officials. There are a lot of things to consider operationally to make sure that the site was truly ready for patients."

CVS' own nurse practitioners and pharmacists are doing the testing in Massachusetts, Goode said. The company closed the store to increase safety and make operations easier, he said.

At the test site, people will drive to different stations in their car. They will first get a temperature check. If they have a fever, they will go to a registration station and get a number that's attached to their test kit to later look up results.

After registration, they will go to a station where a health-care professional puts a swab up their nose. The nasal swab will be wrapped in three plastic bags and refrigerated to keep it safe when it's transported to the lab, Goode said. A private lab, which is not owned by CVS, will do the testing and deliver a result in about 48 hours, he said.

All employees will be in protective gear, he said.

He said CVS is still getting the new site up and running, but it expects to do 12 tests per hour. It will be open from 8 a.m. to 8 p.m., he said.

CVS has not announced when or where it may add more sites and open testing to the public. "We are going to learn from this site before we take this to other locations," Goode said.

In an interview on "Mad Money" with Jim Cramer on Monday, CVS Chief Executive Larry Merlo explained why the company wanted to pitch in to fight the pandemic.

"We ask ourselves every day, 'Is there more that we can do?'" he said. "I think we're in the early stages. I think we've seen from Dr. Fauci and other clinicians that we have the risk of this getting worse before it gets better."