A small medical plane crashed in a mountain range outside Ruidoso, New Mexico , before dawn Thursday, killing all four people aboard and sparking a wildfire in the surrounding forest, officials said.

The fire had grown to 35 acres (14 hectares) by midday amid dry, windy conditions, according to Lincoln County Manager Jason Burns. Burns said county officials were “very concerned” about the blaze and local agencies were working with the U.S. Forest Service to contain it.

The cause of the crash was unknown, Burns said. The plane was located between 8 a.m. and 9 a.m. Thursday in steep, rocky terrain in the Capitan Mountains that was difficult to access, with crews hiking the last half-mile to reach the crash site, he said.

The victims were flight crew and medical personnel, Burns said.…