Four containers containing uranium hexafluoride did not leak after they were dropped about 20 feet on a ship in the Halifax harbour.
The cylinders were being moved from the ship to the dock when they fell and landed in a contained portion of the ship, city staff said in a release early Friday.
The immediate area around the dropped cylinders was evacuated after testing showed radioactive levels were three to four times normal, but fire officials said there no other materials on the ship would be affected.
There were no injuries and all employees on site have tested negative for radiation contamination.
Experts from Toronto are expected at the scene Friday to do a more detailed assessment.