Church bells in Lac-Megantic tolled 50 times on Saturday, once for each person believed killed in the train disaster last Saturday. Other ceremonies took place across the country.
A further five bodies had been found in the ruins of the town, bringing the total number known to have died to 33. Many are yet to be identified.
The BBC reports at least 17 others are still missing and presumed dead.
A small candlelight vigil was held at Saint Agnes church, near the site of the crash on Friday evening.
At midday on Saturday, people gathered on the steps of the church, where the bells were tolled 50 times.
In Montreal, about 200 people attended a ceremony at Notre Dame Basilica.
The Montreal Gazette said events were planned in more than 50 towns and cities across the province.
The BBC reports the train was carrying 72 cars of crude oil from the Bakken oil region in North Dakota in the United States to a refinery on the east coast of Canada.
It was parked shortly before midnight on Friday in the town of Nantes about 11km away. But it later rolled downhill, gathering speed until it derailed in Lac-Megantic and exploded.
At least 30 buildings were destroyed.
Quebec Premier Pauline Marois on Thursday announced a C$60 million ($US57 million) fund to help people and rebuild the town.
Montreal, Maine & Atlantic Railway chairman Edward Buckhardt said on Wednesday that an engineer who was in charge of driving the train had been suspended without pay, after being accused of failing to set a series of hand brakes.