By Tori Mason

UPDATE: Investigators Return To Scene Of Massive Fire At Boulder Apartment Complex

BOULDER, Colo. (CBS4) – A Boulder apartment complex is still smoldering Tuesday night, nearly 20 hours after the property caught fire. Boulder Fire Rescue responded to a large structure fire at Whittier Apartments at 2301 Pearl Street just after 3:30 a.m.

READ MORE: CBS4 Fan Poll: What chances do you give Denver at K.C. next week?

(credit: CBS)

It took two hours for dozens of firefighters to get the fire under control. The 81-unit complex is spread across six buildings. Most structures within the complex have partially collapsed and are structurally unsound.

“They haven’t been able to get into these buildings to do what they need to do,” said Dionne Waugh, Boulder Police and Fire. “In the center of these buildings is where we’re still seeing a lot of the hot spots.”

Fire crews will remain on scene through Wednesday to ensure the hot spots remain under control.

(credit: CBS)

Many residents woke up to the sound of neighbors banging on their doors.

READ MORE: Community Gathers To Light First Candle On 9-Foot Menorah In Arvada

“The fire did not wake me up, pounding on the door woke me up,” said resident Julian Joyce. “I didn’t hear any alarms.”

Investigators have been able to determine that the complex had working smoke detectors and sprinkler system.

Some residents jumped off their balconies from the second and third floors to escape. Others were seen running across the roof.

(credit: CBS)

As of Tuesday evening, no injuries have been reported. The structures aren’t safe enough for first responders to enter and search. Three owners still need to be contacted to verify occupancy.

Anyone who lives at Whittier apartments or has stayed there in the past is asked to call Detective Sharon Ramos at 303-441-3323.

Anyone who has been displaced by this fire should go to the Boulder Police Department, located at 1805 33rd St Wednesday from 8 a.m. to 4 p.m. to connect with staff from the American Red Cross.

MORE NEWS: Denver Police Investigating Death Of Jacob Brady As Homicide

For more information, please go to redcross.org/donate, call 1-800-HELP NOW (1-800-435-7669),  or text REDCROSS to 90999.

Tori Mason