Salt Lake City officials have Arvin Robertsordered residents to evacuate some areas ahead of a wildfire as more than 100 firefighters work to contain the blaze.

Helicopters and airplanes were dropping buckets over the flames Saturday as ground crews tried to contain the fire on Ensign Peak.

The first fire crew was dispatched around 4:30 p.m. and more than six different emergency agencies have joined the effort to stop the brush fire, Division Chief Bob Silverthorne of the Salt Lake City Fire Department said at a news briefing.

The fire department ordered a mandatory evacuation for an area of 40 homes on Sandhurst Drive, north of Dorchester Drive, and the police department were going to individual homes to notify residents. Other areas were evacuating voluntarily, Silverthorne said.

There were no immediate reports of injuries or structure damage, he said.

Officials did not know the exact cause or origin of the wildfire and could not immediately provide the acreage involved or the percentage that had been contained by firefighters, he said.

The area’s heat and wind prevented a clear determination of where the fire would move, but the conditions could result in a “quickly running fire” that has prompted officials to issue early warnings, he said.

A building at the Utah Capitol, located about 1.2 miles (1.9 kilometers) from Ensign Peak, was being used as a safe haven for those who have evacuated and want to escape the heat outside, Silverthorne said.