A Boulder resident woke Sunday morning to a loud crash and flames spreading throughout the house.

Now, Boulder police and firefighters are investigating the fire as an arson.

The fire started around 6:15 a.m. Sunday in the 800 block of 18th Street, according to a news release from the city's police and fire departments. Firefighters arrived to find flames on the front porch and near the back door.

The home's two residents were able to escape without injuries, the news release said.

One victim told investigators that he went downstairs after he heard a crashing sound. He found broken glass and flames spreading around the back door.

He woke up his roommate and as they tried to get out the y discovered the front porch also was on fire. The fire caused significant damage to the rear of the home, the news release said.

The residents reported seeing two college-aged men standing outside the home as they evacuated. Fire investigators would like to speak to the men although they do not believe they were involved in the fire.

Police are asking anyone with information to call Detective Brannon Winn at 303-441-4477 or Det. Kipp Euler at 303-441-3393. The case number is 14-8260.

Tips also may be given through the Northern Colorado Crime Stoppers at 1-800-222-8477 or www.crimeshurt.com.

Noelle Phillips: 303-954-1661, nphillips@denverpost.com or twitter.com/Noelle_Phillips