A passenger plane has lost a section of its fuselage in mid-air, forcing it to make an emergency landing in the US state of Oregon. The Alaska Airlines Boeing 737 Max 9 turned back 35 minutes into its flight to California after an outer section, including a window, fell off on Friday. All 177 passengers and crew were on board and it landed safely in Portland. The airline said it would temporarily ground all 65 of its 737 Max 9 aircraft to conduct inspections. Boeing said it was aware of the incident and was "working to gather more information". The UK Civil Aviation Authority told the BBC it was "monitoring the situation very closely". Evan Smith, one of the 171 passengers on board, said: "There was a really loud bang towards the left rear of the plane and a woosh noise —- and all the air masks dropped. "They said there was a kid in that row who his shirt was sucked off him and out of the plane and his mother was holding onto him to make sure he didn't go with it." Diego Murillo said the gap was "as wide as a refrigerator". Fellow passenger Elizabeth Lee added: "Part of the plane was missing and the wind was just extremely loud. but everyone was in their seats and had their belt on." Announcing the grounding of the 65 planes, Alaska Airlines' CEO Ben Minicucci said: "Each aircraft will be returned to service only after completion of full maintenance and safety inspections." The flight to Ontario, California, had reached 16,000ft (4,876m) when it began its emergency descent, according to flight tracking data. Images sent to news outlets show the night sky visible through the gap in the fuselage, with insulation material and other debris also seen. Oxygen masks deployed during the incident, which began at 16,000 feet shortly after take-off Other pictures show the seat closest to the affected section, a window seat that passengers said was unoccupied, leaning forward without its cushion. "My heart goes out to those who were on this flight — I am so sorry for what you experienced," Minicucci said. "I am so grateful for the response of our pilots and flight attendants." In an audio clip, the pilot can be heard talking to air traffic control requesting a diversion. "We are an emergency," she said. "We are depressurised, we do need to return back." According to photographs, the affected area was in the back third of the plane, behind the wing and engines. The section of fuselage involved appears to be an area that can be used as an additional emergency exit door by some operators, but not by Alaska. The US Federal Aviation Administration (FAA) confirmed Alaska Airlines Flight 1282 "returned safely... after the crew reported a pressurization issue". Boeing said a "technical team stands ready to support the investigation". The seat immediately next to the broken fuselage was said by passengers to be unoccupied The National Transportation Safety Board (NTSB) is investigating the incident. The Boeing 737 Max has been described as "the most scrutinized transport aircraft in history" after a series of safety issues. The Max was grounded in March 2019 for a year-and-a-half after two of the type crashed in similar circumstances, killing those on board. Aviation expert John Strickland said the Alaska Airlines incident is very different to those crashes, adding since the 737 Max came back into service it had "an enormous safety record". "While we know little evidence of why this section of the fuselage has come out — this has nothing to do with the aircraft being grounded for 18 months," he told BBC News. "But, it is natural Alaska Airlines is taking a cautious approach grounding its fleet" More recently, Boeing said it would increase the pace of 737 Max deliveries after resolving a supply error that required it to conduct lengthy inspections of new planes and its inventory, Reuters news agency reported. About 1,300 737 Max aircraft have been delivered to customers, Boeing data shows. Last month, the FAA urged airlines to inspect Max models for a possible loose bolt in rudder control systems. —BBC