Investigators are trying to figure out what sparked a three-alarm fire that tore through a brand new Alexandria (web|news) Hotel and threatened an adjacent apartment building.

The hotel, located at 6065 Richmond Highway, burst into flames shortly before 9 p.m. Thursday."I never saw a flame like that before. It was very huge," said witness Thomas Perez.

Authorities say the fire was fueled by natural gas, and spread quickly through the brand new Spring Hill Marriott Suites hotel still under construction. Today, all that is left of the hotel is a charred shell. A yellow labrador with a nose trained to detect anything that could have deliberately ignited the blaze along with an agent from the Bureau of Alcohol, Tobacco and Firearms searched what was left of the hotel. "Until we come up with a reason why this happened, it's still under investigation. We won't rule anything out," said Lt. Will Bailey, Fairfax County (web|news) Fire and Rescue. 

More than 12 hours after the blaze erupted, firefighters still had to deal with. Hot spots flared up overnight and firefighters had to contend with flying embers landing in nearby wooded areas and on adjacent buildings, including a seven-story apartment building. The apartment building was evacuated, and no injuries have been reported.

More than 100 firefighters battled the blaze at the four-story hotel. Lieutenant Raul Castillo, a Fairfax County fire department spokesman, says it took firefighters about 30 minutes to bring the blaze under control.

Cars parked several hundred feet away from the fire were covered with soot, grassy spots were burned out and leaves on the trees singed. One firefighter was taken to a local hospital, but was released a short time later.

Launch iWitness Photo Gallery

There was heavy smoke throughout the neighborhood. iWitness pictures show the flames reaching high into the sky.

The loss of the hotel is a blow to the area of Route one, worn down by time. With the construction of the Wilson Bridge, the hotel was to be the cornerstone of upscale change in the area. Those who live and work in the area hope that whatever caused the fire won't deter the progress that was plnned in a community that has waited for it. "We need it. There's not much going on as far as high end hotels. So, I don't know. It's a big loss to the community," said resident Shauna George.

The cause of the fire is under investigation. Damaged is estimated at $2 million.