PORT ARTHUR — In what could be one of the largest spills in a regional waterway in some time, about 420,000 gallons of crude oil has spilled after three vessels collided in the Port Arthur area Saturday morning, the U.S. Coast Guard said.

Officials contained the spill, but were still assessing the scope and cause. They emphasized that the initial estimate could fluctuate, Coast Guard Petty Office Renee Aiello said.

This is a significant amount of oil, she said. If it turns out it is 400,000 gallons, it is quite a significant spill. ... The response is going to take some time.

No injuries were reported from the collision.

The U.S. Coast Guard shut down the port in Port Arthur, a key port for commerce along the waterway, she said. Officials did not yet know how long the cleanup will take, but said the economic impact will be $250 million a day after the port\\\'s second day of closure, according to one official at the port.

So many goods come in and out of there, Aiello said. The (Port Arthur) port is of great importance to Houston.

Shortly before 10 a.m., a towing vessel named Dixie Vengeance was pushing a barge. Meanwhile, a 600-foot tank ship called Eagle Atome had lost power and the pilot was unable to steer it. The ship collided with the barge causing crude oil to leak, said John Plunkett, port captain in Port Arthur.

At least some of the remaining crude oil on the Eagle Atome, owned by AET Tankers, was transferred off the ship, Aiello said. The ship can hold up to 3 millions of crude; officials did not know how much crude was on the ship or how much, if any, crude remained on board.

The tank ship and barge are still engaged, she said.

Responding to the spill are two 25-foot response boats, an 87-foot Coast Guard Cutter, Manowar, a helicopter from Houston and extra manpower from the U.S. Coast Guard.

Port Arthur police reported an evacuation of a six-by-five-block area because of a leak of hydrogen sulfide, said patrol sergeant Chris Segler. He was unsure how many people were evacuated, but said most of the area was unoccupied.

City officials opened a shelter at St. John’s, a church in the 500 block of 53rd St.

Residents were allowed to go home Saturday evening. Mike Free, a battalion chief with the Port Arthur fire department, said he didn’t know when the ships would be separated, but officials would re-evaluate whether to order another evacuation then. He said the vessels were not expected to be separated Saturday night. The Port Arthur spill is much smaller than the 11 million gallons spilled in Prince William Sound when the Exxon Valdez ran aground in 1989. One of the worst shipping accidents in the area was the June 1990 spill from the Norwegian tanker Mega Borg. It leaked 4.3 million gallons of crude oil about 60 miles off Galveston.

The Associated Press contributed to this report.