Several people called 911 after smelling a strange odor on the 2900 block of Willow Street near Philips and St. Augustine Road.

"Our hazardous material team took readings and found unusually high levels of carbon monoxide in four of the apartments," Jacksonville Fire and Rescue spokesperson John Bracey tells WOKV. "The odor was coming from a natural gas line leak and the fix was very simple. It just involved closing the valve."

Bracey says families in two of those apartments were rushed to hospitals in serious condition after the gas leak.

The above ground valve controls natural gas flow to the under ground gas line.

"I'm not certain exactly how the valve was opened," Bracey said. "Whether it was accidental or faulty. That's why he call in the gas company to take care of the mechanics of the valve."

But a spokesperson with the utility TECO Peoples Gas says the dangerous carbon monoxide build-up was likely the cause of a faulty appliance in one of the apartments.

Spokesperson Patrick Ho says the natural gas line was shut off as a precaution to prevent any sort of combustion due to the carbon monoxide levels.

The apartment complex was never evacuated, but a handful of families did spend the night away from home as a precaution.

Ho says natural gas service will be restored to the apartment complex once the cause of the carbon monoxide leak is discovered and repaired.