A fire that broke out at an apartment complex in Harlingen on Monday is under investigation, said Harlingen Fire Chief Rafael Balderas.

The fire happened at the Sierra Apartments, located along the 2900 block of Haine Drive. Officials said nobody was inside the apartments.

"We have an idea where it started," Balderas said. "We have to go in there and actually take a look at all the evidence that we could find in there and come up with a determination. Sometimes it'll turn out to be undetermined, but we're going to try to figure out what it is that occurred."

Firefighters contained the fire to one unit; two other units had smoke damage.

Officials say some residents have been displaced.