BILLINGS - Fire officials spent Thursday afternoon battling a massive blaze at the Conoco Phillips refinery in downtown Billings. The fire broke out just a little before 3:30 Thursday afternoon.

Officials said a tank caught fire, sending smoke and flames into the air. Eyewitnesses tell KULR-8 one of the large tanks on scene fully collapsed.

The good news is no injuries have been reported and Conoco Phillips officials said all contractors have been accounted for. Fire officials said as of about 6 p.m. the focus switched to protecting surrounding buildings that may have suffered some damage from the blaze.

A pulmonologist with Billings Clinic said all the smoke in the air could cause breathing issues for people with chronic asthma or other issues like COPD. They said people with these issues should avoid going outside and monitor their symptoms.

Fire investigators said it may take some time to pinpoint what caused the blaze.

Thick black smoke could be seen from miles away as a refinery fire erupts in a storage container at the Conoco-Phillips about 3:30pm in Billings.

Traffic on I-90 was snarled while onlookers took photos, slowed down, or called others on their cell phone.

Montana Highway Patrol officers remained in the area to make sure traffic was moving along, and witnesses were eager to share what they saw.

"When we pulled up from Laurel it was like a bomb went off" said Tony Sellers.

Seller’s son came with his dad to check on the fire.

"If you've never seen a fire, a refinery fire, it’s intense especially for those at the facility and on the Interstate, but we have good crews here in Billings, and Exxon-Mobil mutual aid from Lockwood" said Garrett Sellers

Ross Bradley saw the smoke from the Albertson’s in the Billings Heights and said,

"I've been up in that big coker before and to see flames as high and as big, you know they have a big job on their hands."

Fire crews said as of 6:00 pm the fire was completely contained.