(CNN) -- The U.S. Coast Guard closed 98 miles of the Mississippi River from New Orleans, Louisiana, southward after a fuel barge and a tanker collided early Wednesday, spilling more than 400,000 gallons of fuel oil.

Coast Guard personnel try to contain a fuel oil spill in the Mississippi River in New Orleans on Wednesday.

The closure -- on what is a major shipping route between the Midwest and the Gulf of Mexico -- could last days, and the cleanup could take weeks, said Capt. Lincoln Stroh, the Coast Guard chief in New Orleans.

The collision between the Liberian-flagged chemical tanker Tintomara and the barge pushed by the tug Mel Oliver happened about 1:30 a.m. Wednesday, splitting the barge nearly in half and dumping more than 419,000 gallons of oil into the river, the Coast Guard said.

The accident happened just north of the massive bridges connecting downtown New Orleans to the west bank of the Mississippi, the Coast Guard said. The tanker was undamaged. See a map of where the spill happened »

The Coast Guard said Wednesday evening that the tug had no properly licensed crew on board at the time of the collision. No injuries were reported, and the National Transportation Safety Board said it has dispatched investigators to look into the accident.

The accident left a sheen of oil over much of the river and its banks. Booms were deployed to contain the oil, and skimmers are being used to suck it off the surface, said Petty Officer Thomas Blue, a Coast Guard spokesman. Watch scenes from the oil spill »

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.

But Wilma Subra, a chemist who advises the Louisiana Environmental Action Network, said the oil could affect wildlife and work its way up the food chain into residents, many of whom fish for subsistence.

"This is a spill that occurred in a very urban area, and it can impact a very large number of people," she said.

The oil, widely used as marine fuel, is heavier than diesel but lighter than crude, and it is likely to stick to rocks, trees and wildlife, Stroh said.

"Some will evaporate with sunlight, but there will be residuals in the waterway which need to be cleaned up," he said.

However, State Department of Environmental Quality officials said the oil is so thick that it could sink, which would complicate the cleanup, the Times-Picayune of New Orleans reported.

The Mississippi is the primary source of drinking water for the region, and workers have deployed booms around intakes for local water systems, said Paul Book, the head of the cleanup effort for barge owners American Commercial Lines.

Water intakes in the oil spill area -- those for Algiers, Gretna, St. Bernard Parish and Plaquemines Parish -- were closed to prevent contamination, though residents there still could get water through their taps because of reserve supplies, the Times-Picayune reported.

A swifter-than-normal current quickly drew the slick downstream. The Coast Guard initially closed 29 miles of the river but expanded that to 98 miles by Wednesday evening, the service said.

The heavy, sticky oil left a "real strong" smell hanging over much of downtown New Orleans, said Carl Bauder, who runs a barber shop near the foot of Canal Street.

The Coast Guard's closure of traffic shut down commuter ferries across the river, said Bauder, who lives in the West Bank neighborhood of Algiers.

"[The oil has] done a lot of damage to our Moonwalk area and down by the aquarium," he said.

Department of Environmental Quality officials said they didn't believe breathing the air near the river would be a problem, adding that emergency personnel were checking the air with portable monitors and hadn't found dangerous hydrocarbon levels, the Times-Picayune reported.

New Orleans is among the largest U.S. ports. More than 30 ships were queued early Wednesday afternoon, waiting to pass through the closed zone, Coast Guard spokeswoman Jaclyn Young said.

Ships approaching the mouth of the river from the Gulf of Mexico were being asked to stay out, Stroh said.

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