WINNIPEG -- Homicide officers were investigating the deaths of two young children Wednesday and were searching a residential neighbourhood for their mother.

Police said a girl toddler and an infant boy were pronounced dead in hospital after being found in critical condition at a Winnipeg home.

Const. Eric Hofley said police received a call about 8 a.m. to check on the well-being of residents at the house. Emergency crews found the two children, who were taken to hospital, but died despite frantic efforts to save them.

Police were looking for the last woman they said was with the children -- their mother, 32-year-old Lisa Gibson.

"Officers, several units are on scene currently looking for Ms. Gibson," Hofley said at a hastily called news conference. "At this point, we are concerned for her well-being. We want to make sure that she's fine and obviously, once located safely, we'll be looking to speak with her regarding the incident."

Gibson's Facebook page was full of pictures of her children, curly-haired Anna, age two, and Nicholas, almost three-months old. The page said Gibson works at Concordia Hospital in Winnipeg. Her last posting appeared to be a photo of her daughter reading a newspaper.

"Man I love this kid," the caption read. "She gets me!"

Some friends posted messages on the Facebook page as police continued their search. "My thoughts and prayers are with you. I hope you are ok!" wrote Laura Jean Woodman.

"We love u I hope ur alright," said Breanne Lefort.

Most of the page appeared to have been taken down Wednesday afternoon.

Reports suggested the children were found in the bathtub of the home, but police wouldn't confirm how the children died.

"This is a tragic -- beyond tragic -- incident," Hofley said. "Our thoughts (are) for the family, for friends, for emergency personnel that deal with these sorts of things. All these people will have to move on and our thoughts are with those people."

Police closed off the neighbourhood around the home and were searching the area, Hofley said. They were also concentrating some efforts along the Assiniboine River, which runs near the quiet residential community, he said.

"Members of the Winnipeg paramedic fire rescue are out on the water as well."

People reported seeing Gibson, Hofley said, and anyone with information about her whereabouts was asked to call Winnipeg police.

Neighbour Randy Pittner said the dead children's grandparents were standing on the street outside the home and were crying and distraught.

When he learned what had happened, the single dad felt sick. "I ran to the door and hugged my daughter 'cause ... it's upsetting for everybody."

He said Gibson and her husband moved into the home about two years ago. They were quiet, but friendly, and always had family visiting.

Another neighbour said Gibson worked as a pharmacist but was home on maternity leave.

A spokeswoman for the Concordia Hospital refused to comment on whether Gibson worked there. She said the hospital doesn't comment on human resource matters.