The tanker that struck a cruise ship docked in New Orleans on Friday had a "steering casualty", officials said, citing preliminary findings into the collision.
It remains unclear what caused the steering failure on the Atlantic Asphalt cargo vessel, the National Transportation Safety Board (NTSB) said in a media briefing on Sunday.
The collision left 32 people from the stricken American Heritage riverboat in hospital with non-critical injuries, but no-one was unaccounted for.
The NTSB said there are many different things that could be classified as a steering casualty, and they are "looking at all of them".
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The tanker was upbound on the Mississippi River as it moved toward the east bank of the river just before the collision, said the NTSB, based on findings from the vessel's voyage data recorder.
Minutes before the crash, investigators said audio consistent with the ship's warning system was broadcast, along with commands to deploy the vessel's anchors and emergency ship handling orders.
"We are aware that there was an issue with the steering on board and causing the rudder to remain at a starboard position, causing the heading of the vessel to veer towards the east bank," investigator-in-charge Bart Barnum said during the news conference.
The exact issue with the steering has yet to be determined, he added.
A preliminary report from the NTSB is expected in 30 days.
Calls about the collision began around 13:30 EST (18:30 GMT) on Friday, when people began trying to help passengers escape the boat as it took on water, Port of New Orleans chief Melanie Montroll said after the incident.
There were about 129 passengers, in addition to crew members, on the American Heritage at the time of the collision, according to the port authority.
Passengers began getting off the paddlewheeler vessel, operated by American Cruise Lines, as it started listing before tipping onto its side.
Tugboat operators, police and other rescuers rushed to help while officials shut down traffic in the Mississippi River during the rescue effort.
The American Heritage had been finishing an eight-day cruise calling at destinations in Louisiana and Mississippi along the waterway.
Watch: Cruise ship seen sinking after collision with cargo ship in New Orleans
