The accident happened on the A1 motorway near Estrées-Deniécourt just before midday. The Flixbus coach travelling from Paris to London overturned leaving 33 people injured, including four seriously.
Photos show the coach on its side with the windscreen smashed.
About 50 firefighters, 30 police officers and 10 ambulances attended the scene.
A local police source said: “The bus tipped over for reasons that are being investigated.
“There are foreign passengers on board, as well as French ones. The bus was travelling from Paris to London.
“Many of those on board were treated at the scene, while others were taken to hospitals in the area.
“Of the 33 people on board, four are seriously hurt.”
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“FlixBus is in close contact with the relevant authorities in order to determine the exact cause of the accident and to ensure all passengers receive appropriate support.
“An emergency phone number is available for the passengers and their relatives.”
The company has sent a replacement bus for passengers who are able to continue the journey.