JACKSON (AP) — Mississippi Gov. Haley Barbour said Tuesday that oil from a gushing undersea well in the Gulf of Mexico is hitting the state for the first time.

Barbour said a two-mile long, three-foot wide strand of caramel-colored oil was found Tuesday morning on Petit Bois Island, a barrier island near the Mississippi-Alabama border. The discovery means Louisiana, Alabama and Mississippi have all been hit by oil.

Barbour said vessels will be dispatched to clean up the oil, which is about 35 miles off Mississippi’s coastline.

Barbour said officials believe the strand broke off a patch of oil Sunday south of nearby Horn Island.

‘‘This is no reason for anybody to panic, but it is a reason for everybody to remember that there’s the likelihood there will be more intrusion in some form of depleted oil, tar balls, tar mats, emulsified oil that’s going to reach the barrier islands,’’ Barbour said.

Barbour said additional vessels will be used to gather and absorb oil. He also said flyovers will increase to monitor the oil as it creeps into Mississippi.

Six weeks after the Deepwater Horizon explosion, BP has failed to plug the leak after several attempts. The spill has already leaked between 20 million and 44 million gallons, according to government estimates.

Barbour said the patch of oil should have been spotted Monday but wasn’t — likely because it was beneath the surface of the water.

Barbour said there’s no evidence of oil in the Mississippi Sound, between the barrier islands and the state’s main coastline. While he acknowledged that more oil will likely appear in state waters, he tried to assuage concerns about a catastrophic impact to the region’s tourism and industry.

A Northrop Grumman shipyard in Pascagoula, the state Port at Gulfport, a Chevron Corp. refinery in Pascagoula and numerous casinos make up the bulk of the region’s economy.

‘‘None of them have had any problem operating, even though many of the vessels that call on them come through the Gulf of Mexico,’’ Barbour said. ‘‘I don’t want y’all to jump to conclusions that the port is about to close or the beaches are in danger. We are ready to fight this fight.’’

Bill Glenn, a spokesman for Northrop Grumman, said the shipbuilder has set a 24-hour watch and established a response team at the Pascagoula facility.

‘‘Northrop Grumman Shipbuilding’s main objective is to proactively protect our property and U.S. Navy ships under construction from contamination that may result from the oil spill,’’ Glenn said in an e-mail.

Don Allee, executive director of the Port of Gulfport, said port operations haven’t been disrupted and there have been no reports of vessel contamination.

The oil spill, however, had affected tourism with cancellations ‘‘at a record pace,’’ Barbour said.