A Mexican Navy ship was moving in reverse when it struck the Brooklyn Bridge Saturday night, killing two people and injuring 19 others, federal investigators said.

According to the National Transportation Safety Board, the vessel was attempting to leave port with the assistance of a tugboat when it began drifting in the wrong direction. The NTSB said it remains unclear how or why the vessel ended up in reverse.

Despite the dramatic impact, officials said there was no significant structural damage to the 142-year-old bridge.

“There is some damage on one of the travelers, which they use to access and survey the bridge at this point, but nothing structural from the bridge is an issue at this point,” said NTSB board member Michael Graham.

The ship remains docked in Manhattan. The NTSB is still waiting for approval from the Mexican government to access the vessel as part of its investigation.

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“We are optimistic that we will have that access very soon,” Graham said.

New York police have said a mechanical failure may have played a role in the crash, but Graham declined to speculate. A preliminary report is expected within 30 days.

According to the Mexican Navy, seven officers and 172 crew members who were aboard the vessel have returned to Mexico. Two others remain hospitalized in New York.