Less than two weeks after the birth of two polar bear cubs at Sea World on the Gold Coast, one has died.

The cubs were born on Wednesday April 26 weighing approximately 600 grams and had been expected to be on display to the public in September.

However, Sea World director of marine sciences Trevor Long said concerns about the smaller cub's health were raised on Thursday after it stopped growing at a healthy rate when mother Liya focused her attention on the other cub.

The situation improved on Friday but went downhill again on Saturday.

The smaller cub was then put into an incubator and fed formula as it was underweight and cold, but after 12 hours of specialist care it died during the night.

"Our ultimate aim was to give Liya every opportunity to raise both cubs, however the situation worsened on Saturday morning when it was observed Liya was no longer being attentive towards the smaller cub," Mr Long said in a statement.

The theme park made the announcement through Facebook on Tuesday morning and added the other cub was doing well and bonding with its mother. 

"Despite the best efforts of the veterinarian and animal care teams, sadly one of the cubs passed away," Sea World wrote on Facebook. 

"Whilst it is not uncommon to lose cubs from a litter in all environments, the Sea World team are deeply saddened by the loss.

"The second cub remains in the care of mum Liya and she is displaying positive and confident maternal behaviours towards the cub.

"The Polar Bear team are continuing to carefully observe Liya and the cub 24 hours a day through state-of-the-art monitoring systems and remain cautiously optimistic for the welfare of the cub during this extremely critical period."