OKLAHOMA CITY (AP) — The Oklahoma Highway Patrol says all five people on board were killed when a small passenger airplane crashed in northern Oklahoma on Saturday.

The cause of the crash was not immediately known, said Federal Aviation Administration spokesman Lynn Lunsford.

“A single-engine Extra EA-400 crashed under unknown circumstances … shortly after taking off from Ponca City Regional Airport,” Lunsford said in an email. “The aircraft was destroyed by a post-crash fire,” at the site about 90 miles north of Oklahoma City.

The Extra EA-400 is described as a six-seat corporate aircraft with space for a one-person crew and five passengers.

OHP Lt. Kera Philippi said the fire obliterated much of the aircraft’s tail number.

The Independence Kansas Rural Fire Department reported on social media, “With immense sadness we have lost one of our own from our Montgomery County Rural Fire family. Earlier today Sycamore Firefighter Nicholas Warner, 2 of his sons, his dad Bill, and friend Tim Valentine passed away in an aircraft accident outside of Ponca City Oklahoma.

Our deepest Sympathies go to Brenda, Kaylee, Lisa, Jessica and their entire families and dear friends.”

An OHP report said the plane was northbound from the airport about 10:45 a.m. Saturday when it “lost altitude and stuck the ground.”

The bodies were sent to the Oklahoma medical examiner’s office. All were dead at the scene “due to massive injuries,” according to the OHP report.

Philippi and National Transportation Safety Board spokesman Peter Knudson said the five had flown to Ponca City for a monthly breakfast hosted by the airport.

Airport manager Don Nuzum said the Ponca City Aviation Booster Club hosts a fly-in, drive-in breakfast the first Saturday of each month, but said he could not comment about the crash.

Lunsford said the FAA and NTSB will investigate the crash, with the NTSB leading the investigation.

Knudson said an NTSB investigator was headed to the site Saturday, but it was not known when he would arrive.