WASHINGTON (Reuters) -Southwest Airlines said on Friday it will require passengers to take out removable lithium batteries from powered wheelchairs and scooters before boarding, citing fire risks.

The new rules take effect September 25 and Southwest in January will impose new size limits on lithium batteries. On Tuesday, the Federal Aviation Administration issued a safety alert to airlines over risks from lithium batteries in aircraft passenger compartments, citing a large number of serious incidents.

"Lithium batteries have become one of the most common sources of smoke and fire incidents on aircraft. While these events are rare, quick access and visibility are critical to keeping everyone onboard safe," Southwest said in a note to employees seen by Reuters. "By taking proactive steps now, Southwest will be among the first U.S. carriers to adopt these higher standards."

The FAA on Tuesday recommended airlines adopt risk mitigation strategies, including clear messaging to address potential fire risks tied to lithium batteries carried by passengers and crew members and review firefighting procedures and training.

There have been 50 lithium-ion battery smoke, fire or extreme heat incidents reported this year in the U.S., the FAA said, and some of those have resulted in diversions or injuries.

Southwest said starting Jan. 11 all batteries must be 300 watt-hours or less. The company added it recognizes how important mobility devices are to many customers. "This update is designed to prioritize safety without creating unnecessary barriers to travel," the airline said.