An apartment fire in northwest Harris County significantly damaged four units Thursday.

The fire started shortly after 12 a.m. at the Central Park Regency Apartments on Regency Green Road and Jones Road.

According to investigators, neighbors knocked on the door where the fire started in order to alert the residents.

"They didn't know about it," said Daniel Jimenez. "That's why I was going on all the doors in the complex, in the building. That's why I started knocking on the doors. I didn't know who was home. And if they are sleeping in the middle of a fire, that can do some damage."

Firefighters were able to make a fast attack and quickly extinguished the flames before they spread to more units.

"There is extensive damage to the laundry room," said Richard Ford, with the Cypress Creek Fire Department. "And the first four units on the end and the others have smoke damage to it."

The cause of the fire is not yet known.

No injures were reported.