A rapidly spreading human-caused wildfire in Nevada has injured at least six people and forced around 42,000 residents to evacuate, while tens of thousands more have been warned to prepare to leave.

The Hawk Fire broke out northwest of Reno on Saturday and had spread across more than 15,000 acres (61 square kilometers) by the following day. Three civilians and three first responders have been injured, while several structures have been destroyed.

The “GO NOW” evacuation zone has expanded to the edge of the University of Nevada, Reno, while another 45,000 people in an adjacent “GET SET” zone have been urged to leave and prepare to stay away for several days.

Shifting and strengthening winds caused the fire to change direction rapidly and reportedly jump over fire trucks, preventing crews from reaching some hot spots as residents attempted to flee.

“It was extremely confusing,” Washoe County Sheriff Darin Balaam said, describing how the winds repeatedly sent the flames in different directions and urging residents in evacuation-warning zones to leave. “Please get out if you can right now,” he said.

Officials have determined that the fire was human-caused but have not disclosed how it started or whether it was accidental or deliberate, saying the precise cause remains under investigation.

Footage shared online shows a vast line of flames illuminating the night sky as thick smoke rises over the Reno area. Another video appears to show a man operating heavy machinery while surrounded by flames in an attempt to create a firebreak.

Nevada Governor Joe Lombardo has declared a state of emergency in Washoe County. The National Guard has deployed two helicopter crews and 60 troops to support firefighting operations and protect evacuated neighborhoods. Two hospitals have moved patients to safety, while authorities are monitoring whether the county jail will also need to be evacuated.

Nearly 60,000 customers initially lost electricity, although that figure had fallen to around 10,000 by Sunday. Parts of US Route 395 were also closed.

The Hawk Fire comes as months of dry weather and record-low snowfall last winter fuel blazes across the American West. Fifteen new fires erupted across Nevada on Saturday alone. Earlier this month, wildfires near Spokane, Washington, forced around 60,000 people to evacuate, while three separate blazes north of Reno displaced more than 13,000 residents.