TULSA, Oklahoma - The Tulsa Fire Department is investigating an explosion at an apartment complex Wednesday night.

Firefighters got the call to the Bristol Park Apartments located in the 112000 block of East 45th near Garnett just before 10 p.m.  

Firefighters arrived to find four apartment units damaged and dozens of residents outside in the cold.  

They called Oklahoma Natural Gas to the scene because of a strong odor of natural gas.

Video from Osage SkyNews6 HD showed that the explosion knocked down a wall.  

Tulsa Fire Captain Stan May said the explosion forced the evacuation of 20 residents. He said several residents suffered minor injuries.

Firefighters said the building was at risk of collapsing, so they worked for several hours to stabilize the structure.

The Red Cross provided direct emergency financial assistance to four families totaling 14 people.

TFD said it was looking at the possibility of a meth lab as the cause, but that has been ruled out at this time. The cause still is undetermined.