DALLAS — Updated at 2:01 p.m. with a corrected address.

Thirty residents were displaced after a three-alarm fire early Thursday at a northwest Dallas townhome complex. 

A passerby noticed the fire and called 911 before banging on residents' doors to wake them up and alert them of the fire, fire officials said. 

Firefighters responded after 12 a.m. Thursday in the 9800 block of Webb Chapel Road near Lombardy Lane. 

When firefighters arrived on scene, they noticed flames on the roof of the building, but the blaze had not yet reached the apartments. 

Part of the roof collapsed, according to Dallas Fire-Rescue officials. 

A third alarm was called and 60 to 70 firefighters worked to contain the blaze.

Firefighters saved about half of the nine townhomes. 

It's estimated that four units were damaged by fire, water or smoke, said Dallas Fire-Rescue spokesman Jason Evans.

There is a firewall between each of the townhomes, which helped keep the fire from spreading, Evans said. 

The American Red Cross is assisting 30 displaced residents. No injuries were reported. 

Fire officials say they believe the fire may have started in the attic but the official cause of the fire is still under investigation.

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