WASHINGTON — More than a million small drone aircraft have been sold in the past few years, and a growing number of them are turning up in the skies near airports and airliners, posing a risk of collision. Reports of drone sightings near other planes, helicopters and airfields are reaching the government almost daily, say federal and industry officials.

It’s a sharp increase from just two years ago, when such reports were still unusual.

Many of the reports are filed with the Federal Aviation Administration by airline pilots. But other pilots, airport officials and local authorities often file reports as well, said the officials, who agreed to discuss the matter only anonymously. Michael Toscano, president of a drone industry trade group, said FAA officials also have verified the increase to him.

While many of the reports are unconfirmed, raising the possibility that pilots may have mistaken a bird or another plane in the distance for a drone, the officials said other reports appear to be credible.

The reports underscore the difficulty the FAA faces trying to control drones, which could cause a crash if one collided with a plane or was sucked into an engine. Small drones usually aren’t visible on radar to air traffic controllers, particularly if they’re made of plastic or other composites.

The agency’s near-total ban on their use has been ignored by operators ranging from real estate agents to farmers who use them to monitor crops. Rules to allow broader use of commercial drones are expected to be proposed before year’s end.

“It should not be a matter of luck that keeps an airplane and a drone apart,” said Rory Kay, a training captain at a major airline and a former Air Line Pilots Association safety committee chairman. “So far we’ve been lucky.”

Sen. Dianne Feinstein, D-Calif., said the “reckless operation of drones, whether near airports or anywhere else, is a serious threat to public safety.”

“We shouldn’t wait for a major disaster to take action to protect the airspace,” she said.