NEW ORLEANS — Mississippi River traffic in southeastern Louisiana was shut down Sunday while the Coast Guard led a search for a sunken tugboat believed to have gone down in the middle of the river.

Coast Guard Petty Officer Carlos Vega said 28 southbound and 22 northbound vessels were anchored and waiting for the re-opening of the river; and numerous others not yet in the area would likely be affected. One cruise ship bound for New Orleans was diverted to Mobile, Ala., and contingency plans were being made to do the same for another cruise liner that had been set to reach the city Sunday night.

The Coast Guard closed the river Saturday at 1 p.m. after the sinking of the 48-foot tug C-Pec was reported near the town of Venice. Officials don't know why the tug sank or exactly where but Vega said it was believed to have gone down in the middle of the river. Traffic in both directions was shut down from the mouth of the river to near mile marker 10. It was to remain closed until authorities could locate the tug and determine whether it was a navigation hazard.

"Two people from the sunken tug were reported to enter the river and were rescued by a good Samaritan and transferred to the Coast Guard response boat and taken back to Station Venice," the Coast Guard said in a news release. The names and condition of those rescued were not available.

The U.S. Army Corps of Engineers and local authorities were helping with the search, which included the use of sonar.

Ownership of the downed tug was unclear. The Coast Guard said it was working to find and contact the owner. Online records indicate the vessel was owned by a limited liability corporation with a Belle Chasse, La., address, but the corporation was listed as inactive on the Louisiana Secretary of State website.

Carnival Cruise Lines diverted its ship the Conquest from New Orleans to Mobile on Sunday afternoon and passengers were to be driven to New Orleans.

The Conquest's next trip to the Bahamas has been shortened to a six-day voyage, scheduled to depart Mobile on Monday evening, Carnival said in a news release. Guests scheduled to sail on the shortened trip are being offered a one-day pro-rated refund, or a full refund if they decide to cancel their trip.

The company was making contingency plans in case another ship, the Elation, was unable to reach New Orleans on Sunday night because of the river closure, Carnival spokeswoman Joyce Oliva said in an email.