The landslide, caused by strong rains, hit the vehicle between the villages of Pueblo Rico and Santa Cecilia in Risaralda province, about 230km northwest of the capital Bogota.
"We have already found 33 people dead, including three minors, and we have rescued nine people alive, four of them are in a critical condition," Interior Minister Alfonso Prada told reporters on Monday.
Colombia's President Gustavo Petro described the incident as a tragedy in a Twitter message.
"Solidarity with the families of the victims," Petro said, pledging support from the government.
Pueblo Rico Mayor Leonardo Fabio Siagama told reporters that bodies were being brought to a covered stadium in the town that is normally used for sport.
The bus was travelling from Cali, Colombia's third largest city, to the municipality of Condoto, in Choco province.
Colombia had been hit by an unusually heavy rainy season, blamed on the La Nina weather phenomenon.
Events linked to heavy rains have killed more than 216 people and left 538,000 homeless so far in 2022, according to government statistics.Â
Another 48 people are still missing across the country, the figures show.
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