Dominic Maryk, 7, (top) and his six-year-old sister Abby Maryk have been missing since Aug. 30, 2008. ((Police handout))

Winnipeg police are asking for the public's help in locating two children who have been missing since Aug. 30.

The children, seven-year-old Dominic Maryk and his six-year-old sister, Abby, were on a holiday with their biological father, Kevin Maryk.

They were not returned to their mother, their custodial parent, as planned on Sept. 1.

"If there was any concerns on the guardian parent's part regarding this possibility … she would not have let the children go," said police spokeswoman Const. Jacqueline Chaput.

"There was no indication by the suspect in this matter that the children weren't going to be returned, so therefore the guardian is very concerned right now."

When police went to Maryk's Winnipeg home, they found his belongings had been removed. Chaput said it appears Maryk did not intend to return.

Abby Maryk is described as having green eyes, wavy, shoulder-length, blonde hair and weighing about 40 pounds. Dominic has brown eyes, short brown hair and weighs 60 pounds.

Warrant issued for father

A Canada-wide warrant has been issued for Kevin Maryk, 37. He is described as being about 5-feet-10, weighing about 205 pounds. He has hazel eyes, and most recently had a shaved head and goatee.

They were last seen at a car rental agency in the area of King Edward Street in Winnipeg on Aug. 19, at the start of the authorized vacation.

Kevin Maryk

Police have issued a Canada-wide warrant for Kevin Maryk's arrest on two counts of abduction in contravention of a court order. (Winnipeg Police Service)

Police said they have exhausted all leads in the case, so they're appealing to the public for help.

The vehicle hasn't been returned to the rental agency, police said Friday. Police declined to release a description of the vehicle, saying they don't know if he still has it or where he was headed.

"It's a very generic vehicle, and we're just worried that there would be … an influx of far too many calls in relation to a possible sighting of that vehicle," Chaput said.

"We really want to focus on the descriptions and what he looks like, what the kids look like, rather than focus on a vehicle right now."

There has been no record of Maryk or the children crossing the Canadian border.

An Amber Alert was not issued because it's not believed the children are in danger, police don't have a confirmed vehicle, and too much time has passed since the children disappeared.

"Investigators at this point do not believe the children are in danger, and that's the biggest, I guess, factor that doesn't meet the criteria for Amber Alert," Chaput said.

A Canada-wide warrant has been issued for Maryk for two counts of abduction in contravention of a court order.

Anyone with information regarding Maryk's or the children's whereabouts is asked to contact the Winnipeg police at (204) 986-6250 or (204) 986-6222 or Child Find at 1-800-532-9135.