Cut the power supply to the entire house to prevent electrocution or fire. Use a dry stick or similar implement to flip the master switch to the off position, first making sure you are not in contact with a wet floor or metal object.
Contact emergency preparedness authorities in your municipality for information on the situation.
If the basement is already flooding
Don't touch anything! Contact Hydro-Québec immediately at 1 800 790-2424 to have the power cut at the meter or pole.
When the flood waters have receded
Consult a master electrician before restoring power, or having it restored, especially if the distribution panel was flooded. He or she will assess the condition of your electrical system, carry out repairs if necessary and, if service was disconnected at the meter or pole, ask Hydro-Québec to reconnect you.