Officials were trying to determine the nationalities of all the victims.
The force is an independent international organisation created by Egypt and Israel to monitor their border in the Sinai after a 1979 peace deal.
It currently includes forces from the US, France, Australia, Canada, Colombia, Fiji, Hungary, Italy, New Zealand and Uruguay, plus a few officers from Norway.
The French-made DeHavilland DHC-6 Twin Otter aircraft crashed in clear sunny weather between 9am and 10am, after taking off from the multinational force's El Gorah base - the northern headquarters of the peacekeeping mission, St Pierre said.
The aircraft was being flown by the French contingent of MFO with what St Pierre described as a "higher than normal" load of passengers and crew.
St Pierre said it was unclear how many people in all were aboard the Twin Otter, but other local, officials said only the nine who died were aboard - four crew and five passengers.
St Pierre said his information on the crash came from local Egyptian authorities who arrived at the scene of the wreckage, and who told force officials that there appeared to be no survivors.