Some 10,000 people in the 62,000-person community were told to leave their homes, bridges and roads were closed and gas was turned off in homes and businesses Sunday, CNN reported.
The South Saskatchewan River is expected to burst its banks early Monday morning, and could reach its highest-ever level in history, the Canadian Broadcasting Corp. reported Sunday.
"We don't want to anticipate the worst, but we're going to be prepared for the worst," Alberta Premier Alison Redford said. "We know that from what we've seen everywhere else that this is more exceptional than we've ever seen in Alberta before, so we're presuming that that's probably the circumstance that we're looking at (in Medicine Hat) as well."
Calgary Mayor Naheed Nenshi said Saturday the city was still under a state of emergency, though the flow of floodwaters was starting to slow and residents could begin returning home.