As many as 100,000 residents of Calgary, Alberta, could face evacuation because of flooding, the director of emergency management said early Friday.

Mandatory evacuation orders have been issued for 20 communities, Bruce Burrell said. Parts of of southern Alberta face rising floodwaters and the possibility of more rain.

The levels of the Bow and Elbow rivers are expected to peak overnight, but not drop until late Saturday at the earliest, he said.

"I have never experienced any flooding of this magnitude," he added.