A blizzard dumping snow across North Dakota and freezing temperatures in Manitoba are adding to flood threats across the southern part of that province, said a government official on Tuesday.

The cold weather, said Randy Hull, emergency preparedness co-ordinator for Winnipeg emergency services, means that no snow is melting and no water being added to the river.

By time the snow dumped in North Dakota on Tuesday melts, the crest of the Red River will have already reached Manitoba.

But the cold temperatures also mean that the ice will stay frozen on the river.

"The longer the ice is there, the more chance there is the ice jam when we have the peak," said Hull.

This means there is still a flood risk in southern Manitoba. Ice jams in rivers, blocked drains and frozen culverts could still cause overland flooding this weekend if the cold weather continues.

The city of Winnipeg is taking no chances. They have already told some homeowners to build dikes and have put about 140 homes under flood-protection as of Tuesday afternoon. They've also started a volunteer registration program, so people who have run out of friends and family can have help building dikes around their homes.

The peak of the river is now expected to hit six metres in Winnipeg over the weekend. Such a rise would normally be manageable, said Hull, if there wasn't any ice on the river.

But there is ice on the river. And last Friday, it was two feet thick.

This combination, said Hull, means there's "very serious potential for ice jams at two locations in the city. And if you had a quick rise of even three or four feet, we have some areas that would be problematic for us."

A rise like that is probable if there is an ice jam, warned Hull.

Hull added there would be evacuations if the flood reached that high. "We have to wait and see what the river might do in the coming days."