PROVIDENCE, R.I. (AP) – The Coast Guard reopened the Port of Providence to marine traffic Wednesday with a safety zone around the site of a massive fire that erupted where a tanker was unloading gasoline.

It was still not clear Wednesday if the fire, which happened in a dock area, was caused by lightning that struck nearby. Coast Guard Petty Officer Luke Pinneo said authorities were investigating other factors that may have contributed to the blaze late Tuesday, although he would not say what they were.

A truck driver told The Associated Press on Tuesday night that he saw lightning hit near the dock, then an explosion and large fireball.

No injuries were reported.

Coast Guard officials said the 600-foot Nord Europa, a Danish ship, was able to safely pull away from the dock after the explosion and was anchored at Jamestown on Wednesday.

The blaze had been largely contained by early Wednesday, but Pinneo said firefighters were still battling hot spots that flared up occasionally.

The fire happened at a terminal run by Motiva Enterprises, a Houston-based joint operation between Saudi Refining Inc. and Shell Oil Co.

The port was closed for several hours after the fire. It reopened Wednesday, but vessels were not being allowed to pass through a 100-yard zone around the Motiva facility.

Brian Delaney, a spokesman for Motiva, said the company was making arrangements with its other facilities in New Haven and Bridgeport, Conn., to provide alternative storage facilities for its customers.

Motiva supplies fuel to wholesalers, but Delaney said he hoped the fire would not significantly affect the gas supply in Rhode Island.

Gail Mastrati, a spokeswoman for the Department of Environmental Management, said despite some spillage from the ship, environmental officials were not concerned about environmental damage.

There was a fine sheen of fuel on the water Wednesday morning, but Mastrati said it was too little to be collected and some of it had already evaporated. She said federal environmental officials also tested the air quality and did not find any problems.

Multiple lightning strikes on Tuesday night knocked out power for thousands of people around the Ocean State. National Grid said about 4,000 customers remained without power Wednesday afternoon.

AP-ES-07-19-06 1536EDT