One of two cubs born recently to a polar bear at the Toronto Zoo has died, and its surviving sibling is in intensive care, officials said Friday.

Officials revealed this morning that Aurora — one of two female polars at the zoo — gave birth to two cubs on Nov. 11 but that one of them died within 24 hours.

"Aurora demonstrated good maternal instincts and her cubs did attempt to nurse, but it appears she was not producing any milk to feed her newborns," said Eric Cole, manager of wildlife care, in a statement.

The surviving cub was moved to an intensive care unit to improve its chances. It will be given intravenous fluids and special milk formula developed by the zoo.

"This is an extremely critical time for this tiny cub and zoo staff are providing 24/7 care," said Dr. Chris Dutton.

"So far [the cub] appears to have responded very well to the treatments."

The zoo is part of a larger research project into polar bear reproduction.