LOS ANGELES -- A small plane crashed Saturday near a municipal airport in the US western state of Utah, killing all four people on board.

The single-engine Cessna 172 crashed near St. George airport at around 6 a.m. local time (1300 GMT) Saturday about 400 feet (121.92 meters) from the runway, local TV station reported.

The wreckage was found by an airport crew making a routine safety check of the property. St. George city spokesman Marc Mortensen says it's uncertain whether the crash occurred shortly after takeoff or upon landing.

The airport has been in operation at its current site for about one and a half years. It does not have a radio tower and pilots use an automated system to communicate with one another when landing or taking off, Mortensen said.

According to Ian Gregor, the Federal Aviation Administration (FAA) Communications Manager, the plane crashed under "unknown circumstances."

Federal authorities are investigating the cause of the crash. The investigators from the FAA and National Transportation Safety Board were expected to arrive at the site later Saturday, Gregor said.