WILLISTON, N.D. (AP) — Cleanup efforts at the still-smoking site of an oil field supply company in North Dakota that caught fire earlier this week could take weeks, an Environmental Protection Agency Official said Friday.

EPA On-Scene Coordinator Paul Peronard said it would not surprise him if it took two months to clean up the site in Williston, though workers are hoping it will be quicker.

Officials say the fire started about midnight Monday and burned most of Tuesday. At its height, the blaze sent fireballs hundreds of feet into the air.

The Red River Supply facility stored dozens of chemicals used by oil companies, according to state records. The cause of the fire has yet to be identified.

Peronard said workers had not yet started to clean up the main debris field as they give investigators time to identify the cause of the fire. He said once debris clearing begins, workers expect flare ups because a number of volatile chemicals remain.

On Friday afternoon, burned out semi-trucks could be seen in the debris field alongside charred chemical containers. An acrid smell hung in the air and parts of the site were still smoking.

"It could stay and smolder for months if left to its own devices," Peronard said.

Some contamination found its way into a storm water runoff next to the site, but the runoff was closed off during the incident. A U.S. Fish and Wildlife representative was on scene collecting fish for testing.

Peronard said he believes chemicals may have taken up much of the oxygen in the water, killing the fish. Cleanup workers are injecting oxygen into the storm runoff.