Phones, power banks and vapes are spontaneously catching fire on planes, injuring passengers and disrupting flights. Minutes after Alaska Airlines Flight 2117 had lifted from the runway, a phone and power bank sitting in a passenger's lap burst into flames.

The fire scorched the passenger's arms and legs before she tossed the devices into the aisle, where flight attendants scrambled to get them into a fireproof bag to quell the blaze. Pilots declared an emergency, dropped oxygen masks in the cabin, and turned back to Wichita, Kan.

The incident from earlier this year is just one example of what airlines and regulators say is the fastest-growing safety threat to air travel—phones, power banks and vapes spontaneously catching fire midflight. Those and other personal devices have lithium-ion batteries, which are prone to bursting into flames when they malfunction or overheat.

While the threat isn't new, the industry's assessment of the risks has heightened as passengers bring more devices onboard.