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(CNN) -- Colorado Gov. Bill Ritter declared a state of emergency Tuesday as firefighters battled a 7,100-acre blaze near Boulder that threatened hundreds of homes and forced thousands to evacuate.
Ritter said the state was throwing $5 million into the battle to save homes and forests in the Fourmile Canyon area west of Boulder.
"It is important right now for people who've been evacuated to just be patient," Ritter said after a tour of the area. "This is a very volatile situation, it would be fair to say. There is a fire line. They are doing all they can to contain the fire line. At the same time, there are a fair number of embers that are also starting smaller fires."
Ritter said he saw "entire hillsides" burned by the flames, along with numerous structures.
"It's not safe for people to return to their homes, because as we drove up there, you go from a place that is relatively safe, and then suddenly, you'd see a spot fire burning on the side of the road," he said.
Boulder County Sheriff Bob Pelle accompanied the governor on his tour of the area and said the fire had "literally exhausted our local resources and management team."
"But we have a good and healthy amount of people in place now learning everything they need to know about the fire," he said.
The men and women battling the fires on the ground have gotten a boost from the skies. Tankers and other aircraft that were grounded most of the day Monday by 40 mph winds were in the air early Tuesday as the winds diminished.
The sheriff said his department was investigating a report that the fire may have started when a car hit and ruptured a propane tank.
"That's the best information I have right now, but that's part of what that investigative team is doing for me today, is trying to lock all that down and confirm it," he said.
Pelle said that authorities had evacuated 70 subdivisions and made nearly 8,000 notifications. No injuries have been reported.
"We did mandatory evacuations, but we still had people who didn't leave," Sheriff's Office Cmdr. Rick Brough said earlier in the day. "There's many subdivisions up there."
Brough and Pelle said they did not have a good count on the number or type of structures destroyed so far in the fire.
The fires meant no classes Tuesday for students who attend mountain schools in the Boulder Valley School District.
"Mountain schools include Jamestown, Gold Hill and Nederland elementary schools, as well as Nederland Middle/Senior High School," the district's website said.
Excel Energy said early Tuesday about 1,200 people were without power because of the fire.
CNN's Amanda Watts, Dave Alsup and Erica Henry contributed to this report.