American Airlines and United Airlines announced Thursday they will add more flights in July amid improving demand, suggesting the industry had seen the worst of the hit from the coronavirus shutdowns.

Citing increased interest from consumers in US states that have reopened more quickly from the restrictions imposed to contain COVID-19, American will fly 55 percent of its domestic schedule in July and nearly 20 percent of its international schedule.

"We're seeing a slow but steady rise in domestic demand. After a careful review of data, we've built a July schedule to match," said Vasu Raja, American's senior vice president of network strategy.

"Our July schedule includes the smallest year-over-year capacity reduction since March."

Later Thursday, United Airlines said it was reinstating in July flights at over 150 US and Canadian destinations, increasing non-stop flights from Chicago, Denver, New York and its other four hubs.

"Many customers have told us they are considering flying again," United said, adding that capacity will still be down 70 percent in July compared with the year-ago period.

Major airlines have been slashing service and encouraging flying staff to take unpaid leave to try to conserve cash after demand dropped by as much as 95 percent as the pandemic hit.

But American, which has a higher debt level than other leading US carriers, said it had an average of 110,330 customers in late May, more than three times the level from April.

Its planes were 55 percent filled by late May, up from 15 percent in April.

American said it would boost service to parts of the US where demand was strongest, including Florida, North Carolina, Georgia and South Carolina. The carrier also added more flights to Colorado, Utah and other western states with national parks.

The announcements boosted airlines shares, with American leaping 41.1 percent to end the day at $16.72, and United gaining 16.2 percent to $39.10.