Hurricane Ida damaged a grain export elevator owned by global grain trader Cargill Inc., and rival shipper CHS Inc. warned that its grain facility may lack power for weeks after the storm tore though the busiest U.S. grains port.

The news rattled the markets at a time when global grain supplies are tight and demand from China is strong. Chicago Board of Trade grain and soybean futures slumped to their lowest prices in weeks on Tuesday. The shipments from the Gulf Coast account for about 60% of U.S. exports.

"There's plenty of uncertainty about the Gulf," said Jim Gerlach, president of brokerage A/C Trading. "Nobody knows if it's something that's going to last for days, weeks or months."

Minnetonka-based Cargill said its Reserve, La., terminal, one of two the company operates along the Mississippi River near the Gulf of Mexico, "sustained significant damage" when the storm roared ashore.

Rival crop exporters Bunge Ltd. and Archer-Daniels-Midland Co. said they were working to assess damage to their export facilities in the area.

The Cargill terminal's grain conveyor system partly collapsed.

"This area in SE Louisiana is still facing significant personal safety concerns and power outages, so we are just able to start assessing the storm's impact on the river system. We don't currently have a timeframe for resuming operations," Cargill said in a statement.

CHS — the nation's largest farmers cooperative, which is based in Inver Grove Heights — is working to divert export shipments scheduled through the next month to its terminal in Kalama, Wash., as the hurricane knocked out a transmission line that powers its Myrtle Grove facility south of New Orleans, the company said Monday.

"Best estimates as to when power will be restored at the terminal are in the two- to four-week range," said John Griffith, executive vice president at CHS Global Grain & Processing.

A preliminary assessment of Bunge's Destrehan export terminal and oilseed processing plant found no significant structural damage, spokeswoman Deb Seidel said.

Bunge had hoped to restart operations on Tuesday after shutting down on Saturday ahead of the storm. But power to the facility remains out with no estimate for when it may be restored, Seidel said.

Archer-Daniels-Midland will assess damage to four New Orleans grain elevators and port operations it closed over the weekend ahead of the hurricane, spokeswoman Jackie Anderson said.

"ADM has a vast transportation network and we are making alternate shipping arrangements as necessary to meet customers' needs as we manage through this difficult situation," she said in an e-mail.