The largely arid province, Shanxi, has reported more than five times its usual rainfall since the start of the month, resulting in the destruction of dams and rail lines, reports said.
Authorities in Hebei province said in a social media post that 37 of the 51 people on the bus had been rescued. State broadcaster CCTV said that three had died, and 11 were missing.
According to Shanxi's emergency management department, 1.75 million people have been affected and more than 17,000 buildings collapsed so far due to the floods.
The vast majority of the victims were in Zhengzhou, the provincial capital, where 292 died and 47 are missing.
People told to stay away from rivers, canals and big tanks for the next few days
Typhoon Megi brought torrential rain and strong winds, destroying hundreds of houses and shutting down airports and railways.