(CNN) — The U.S. Coast Guard has closed 29 miles of the Mississippi River from New Orleans southward after a tanker and a barge collided, spilling more than 400,000 gallons of fuel oil into the river. The river, a major shipping route between the Midwest and Gulf of Mexico, could be closed for days during the cleanup, the Coast Guard said Wednesday.

More than 30 ships already are queued up along the river, waiting to pass through the closed zone, Coast Guard Petty Officer Jaclyn Young said.

The Coast Guard has deployed 45,000 feet of inflatable booms to contain the spill and is lining up another 29,000 feet, but it could be days before the river is reopened, she said.

The accident left a sheen over 90 percent of the area, she said.

However, the spill is much smaller than the ones that followed Hurricane Katrina in 2005, when the Coast Guard estimated that more than 7 million gallons of oil were dumped into the Mississippi and nearby waterways.

The collision between the Liberian-flagged chemical tanker Tintomara and the barge pushed by the tug Mel Oliver occurred about 1:30 a.m. CT (2:30 a.m. ET) Wednesday, resulting in more than 419,000 gallons of oil spilling into the river, Young said.