(CNN) -- A raging wildfire that swelled within a day to 8,000 acres in northern Colorado, burning structures and forcing evacuations, showed "significant growth" overnight, fire officials said Sunday.
"Fire behavior and fire weather has not been our friend," Larimer County Sheriff Justin Smith said late Saturday.
A new acreage estimate for the fire was not immediately available Sunday. Nick Christensen of the Larimer County Sheriff's Office told reporters Sunday authorities were working to get an aircraft up to provide a better estimate.
Firefighters battled the blaze, dubbed the High Park fire, that has been fanned by high temperatures and dry brush since it began Saturday morning 15 miles west of Fort Collins, according to InciWeb, the U.S. multi-agency Incident Fire Response website.
Eighteen structures are lost or damaged, with others threatened, InciWeb said. There were no immediate details available about the type of structures destroyed.
Additional evacuations were ordered early Sunday in the area. An emergency shelter was established at a middle school in La Porte. A highway in the area was closed.
About 1,600 phone lines in the area were contacted, Christensen said, but did not know how many homes were included in the evacuations. Evacuating those in danger was authorities' number-one priority, he said.
At least 250 firefighters, along with air tankers and helicopters, were battling the blaze, officials said.
Cooler conditions were in place Sunday, but were not expected to impact firefighting operations, Christensen said. The growth of the blaze remains a source of concern, he said.
Smith said his agency and local firefighters went door to door to make sure people got out safely as the blaze consumed acres of land west of Fort Collins.
In one case, a wedding party was forced to flee as the flames moved closer.
Compounding the problem is a shortage of resources, Smith said. He said a lot of regional resources are already deployed fighting other outbreaks, such as the Whitewater Baldy fire in New Mexico.
The cause of the fire is under investigation, officials said.