A fierce wildfire raging near Boulder in northern Colorado has scorched more than 7,100 acres (2,873 hectare) of vegetation, forcing 3,500 residents to evacuate as the authorities has put the area under a state of emergency Tuesday.

Govenor Bill Ritter declared a state of emergency, saying the state was throwing 5 million dollars into the battle to save homes and forests in the Fourmile Canyon area west of Boulder, CNN reported. Federal emergency authorities have also promised a federal firefighting grant.

"It is important right now for people who've been evacuated to just be patient," Ritter said after a survey of the burned area. "This is a very volatile situation."

The fire, which was started on Monday morning in the 7100 block of Fourmile Canyon Drive, in foothills about 6 miles(9.6 km) west of Boulder, has doubled in size by Tuesday afternoon as over 300 firefighters from more than 35 fire departments and agencies, including the U.S. Forest Service and the Colorado State Forest Service and backed by seven air tankers, have engaged in a tough attack throughout the night. Thick smoke plumes can be seen as far east as Denver International Airport.

Command of the fire was turned over to federal agencies on Tuesday afternoon, which will bring additional crews, expertise and money, Laura McConnell, the local incident command spokeswoman said.

At least 92 structures have been burned down, authorities said after a preliminary survey of the affected area. The fire, fanned by 45-mph(72 kph) strong winds, had also burned the homes of at least nine firefighters.

More than 3,500 local residents have been evacuated. Luckily, no one was injured.

Smoke from wildfires can induce asthma and worsen chronic heart and lung disease,the Colorado Department of Public Health and Environment cautioned in an advisory. Residents are advised to close air conditioners' fresh air intake or find shelter elsewhere as the smoke contains a mixture of gases and fine particles from burning trees and other plant material.

Local hospitals have begun receiving patients complaining of respiratory problems related to the smoke, and more are expected as the fire continues to spread.

No portion of the fire has been considered contained so far, Boulder County Sheriff's Commander Rick Brough said. It could be at least a couple of more days before the situation could be put under control, he added.

The cause of the flame has remained under investigation, the authorities said.