By Rebecca Ballhaus

The Trump administration unveiled Thursday a $750 million deal to buy 150 million rapid Covid-19 tests from Abbott Laboratories, a move that would substantially expand the nation's capacity for rapid testing.

The Food and Drug Administration on Wednesday granted emergency-use authorization to the company for a $5 rapid-response Covid-19 antigen test that is roughly the size of a credit card. The test could be administered in a doctor's or school nurse's office and uses technology similar to home pregnancy tests. It returns results in about 15 minutes.

"This is a major development that will help our country to remain open, get Americans back to work and kids back to school," White House senior adviser Alyssa Farah said.

The White House announcement comes as President Trump is expected to tout his response to the pandemic that has claimed roughly 180,000 American lives in his speech Thursday at the Republican National Convention, where he will formally accept the party's presidential nomination for the second time.

Abbott said Wednesday it plans to ship tens of millions of the tests in September and expects to increase production to 50 million tests in October. The October total would be roughly double the number of tests performed in the U.S. in July.

Abbott said its data show the new antigen test has demonstrated sensitivity -- the percent of positive cases a test accurately detects -- of about 97%. Rapid antigen tests are generally thought to be less sensitive than lab-based PCR tests.

The White House has long used a different rapid test created by Abbott to test the president and those who come into contact with him. The company has come under scrutiny for that test. It was forced to revise instructions for use of the test when a preliminary study by a major medical center found that it frequently gave false negative results.

Abbott shares rose almost 8% Thursday, boosted by the emergency-use authorization and news of the large White House purchase.

Write to Rebecca Ballhaus at Rebecca.Ballhaus@wsj.com