Flames spread across more than 100 mountainous acres north of the U.S.-Mexico border Saturday afternoon, although the Otay Mesa land is isolated enough that no neighborhoods appeared to be in immediate danger.

Cal Fire Capt. Mike Cornette said the fire may take several days to extinguish.

Vegetation began burning around 3:10 p.m. near the Otay Mountain Truck Trail.

Officials initially estimated the fire to be about 4 acres. Within a few hours, the size had grown significantly, and Cal Fire posted videos online showing helicopters dumping water over smoking terrain.

The closest group of people to what’s being called the Border 58 Fire appeared to be those in the Richard J. Donovan state prison, several miles west of the truck trail, but Cornette said Saturday evening the fire was moving east.

No injuries or property damage had been reported and there were not yet any evacuation warnings.

The cause of the fire remains under investigation.

San Diego County is currently under a heat advisory and some desert communities are expected to top 110 degrees. Much of the region has also seen vegetation bloom from heavy rains earlier in the year.