Three people are missing after two barge towing vessels collided Sunday on the Mississippi River in an accident that also may have released toxic vapor into the air, the Coast Guard said.

The Coast Guard said in a news release that the two vessels collided Sunday morning near Luling, Louisiana.

The towing vessel, RC Creppel, sank, and three people aboard are missing. A fourth person was rescued by a private boater.

The RC Creppel was pushing two barges carrying sulfuric acid and the barges broke away during the accident. One of these barges was damaged in the incident and reportedly released an unknown amount of vapor into the air, the Coast Guard said. The immediate area was closed to vessel traffic as a safety precaution.

“This is a complex response that has a search-and-rescue component, as well as a pollution component that will require planning and coordination to execute,” Capt. Kristi Luttrell, the Commanding Officer of Sector New Orleans said in a statement.

“We are working alongside our partners at the state and local levels to quickly assess the situation so that we can safely make every effort to find the missing mariners and minimize any further impact to the environment.”

The other towing vessel involved in the accident is named the Cooperative Spirit.