Passengers on board United Airlines flight from San Francisco to Honolulu, Hawaii, got quite a scare Tuesday when the covering of an engine flew off mid-flight. Flight UA1175 sent out a distress alert on its approach to Hawaii and made an emergency landing safely after the incident.

In a statement to Business Insider, United Airlines said: "United flight 1175 traveling to Honolulu from San Francisco landed safely after the pilots called for an emergency landing because of a loss of the engine cowling (the covering of the engine). Our pilots followed all necessary protocols to safely land the aircraft. The aircraft taxied to the gate and passengers deplaned normally."

Photos and videos posted on social media by several passengers on board showed the cover ripping off the Boeing 777-222 airplane’s engine mid-air, with its inner parts eventually becoming more exposed.

"That looks bad," wrote Erik Haddad, one of the Twitter users. "Plane and simple." He also posted a video of the parts peeling off.

"Scariest flight of my life," Maria Falasch, another passenger tweeted alongside several photos of the exposed engine.

The United Airlines flight was said to be about 40 minutes away from its destination Honolulu when the incident occurred, KGMB-TV, CBS-affiliated television station reported.

The news outlet also posted a clip out of the audio between the pilot of the flight and air traffic control in Honolulu in the moments before the plane landed:

Pilot: "If you haven't already, roll the fire trucks."

Air traffic control: "They will be standing by."

United Photos and videos posted on social media by several passengers on board showed the cover ripping off the Boeing 777-222 airplane’s engine mid-air. In this photo, a United Airlines flight is pictured taking off from San Francisco International Airport as it travels to Honolulu, Hawaii, Nov. 7, 2017. Photo: Getty Images

"There was a loud bang…and then the plane really started shaking," passenger Allison Sudiacal told the outlet. "There was a loud boom and then it was like rattling and the plane was kind of shaking like boom, boom, boom." 

Sudiacal was traveling with her 4-month-old-son on the flight.

"They let us know that we had to brace for impact in case there was a rough landing," she added. "It was scary. But they did a really good job."

The reason behind the incident was still unclear as of Tuesday night. The National Transportation Safety Board said it would be sending a "team of 2" to conduct an investigation into the incident.

"No injuries reported, flight landed safely at Honolulu Airport," the agency tweeted.