A Canada-wide warrant has been issued for a Winnipeg woman wanted in the case of two missing children.

Police say Sandra Giesbrecht, 44, may have the two children with her, after a caregiver reported them missing on Monday.

The nine-year-old boy and 11-year-old girl went missing on Monday evening, Winnipeg police said. They were last seen leaving the home of a caregiver and getting into a white four-door vehicle, while accompanied by someone known to them.

Police said Wednesday the children are believed to be with Sandra Giesbrecht, and the case is being treated as a possible abduction.

"While police are not concerned necessarily for the well-being of the children, they are considered missing at this point and we do need to locate them," Const. Rob Carver told reporters on Tuesday.

Police must have reason to believe a child is in imminent danger before issuing an Amber Alert.

Winnipeg police are working with the RCMP on the search effort, and are considering the possibility the children may have been taken out of the province.

With files from CTV Winnipeg