The U.S. National Transportation Safety Board (NTSB) has determined the an Alaska Airlines jet's mid-air blowout on Friday was an "accident" rather than an "incident."

Jennifer Homendy, chair of the NTSB, said some people sustained minor injuries. "We are not aware of serious injuries, but it was terrifying," she said at a press briefing on Saturday night.

No passengers were seated next to a cabin panel that blew out, she told reporters. "We are very, very fortunate here that this didn't end up in something more tragic."

A piece of fuselage tore off the left side of the jet as it climbed following takeoff from Portland, Oregon, en route to Ontario, California, on Friday, forcing pilots to turn back and land safely with all 171 passengers and six crew on board.

Images shared on social media showed passenger oxygen masks hung from the roof next to a missing window and a portion of a side wall of an Alaska Airlines Flight 1282. 

In response, the U.S. Federal Aviation Administration (FAA) on Saturday issued a directive temporarily grounding certain Boeing 737 Max 9 airplanes for inspections, with several airlines in the U.S. and beyond taking similar actions. 

In a statement, Boeing said it supported the FAA's decision and was co-operating with the NTSB's investigation. "Safety is our top priority and we deeply regret the impact this event has had on our customers and their passengers." 

It is the latest problem involving Boeing's 737 Max model, which was grounded for 20 months worldwide after two fatal crashes in 2018 and 2019 linked to poorly designed cockpit software killed 346 people in Ethiopia and Indonesia.

(With input from Reuters)