Key Points:

Two critically endangered Sumatran tiger cubs have been born at Auckland Zoo, after 10 years of planning and preparation.

Auckland Zoo staff today said while they were excited at the arrival there were still many risks involved for the survival of the cubs.

Keepers arrived at work on Thursday to the "squeaking" of what was thought to be one tiger cub, born in the early hours of the morning to Molek.

But when they came back later in the morning, they realised there were two cubs.

Keepers are yet to get a close look to confirm details, preferring to leave the cubs and its mother to bond, but believe all seems to be going well so far.

Auckland Zoo carnivore team leader Andrew Coers said Molek, who is eight, had come to motherhood quite late in life.

Molek has also started eating again - something she stopped a few days before birth and immediately after .

"The birth is a highlight of the conservation efforts of the zoo to help this critically endangered tiger," said Mr Coers this morning when it was believed there was only one cub.

"It's great to finally have a Sumatran tiger cub at Auckland Zoo. The cub is particularly genetically valuable as two-year-old dad Oz's bloodline is not represented in Australasian or European zoos."

Mr Coers said Molek would determine when the cub goes on display but it could be up to eight weeks away.

People will be able to see both mum and cub via a "cubcam" (that links to their inside den) at the tiger exhibit, over the next few weeks.

Zoo spokeswoman Jane Healy said pictures would be available soon but keepers did not want to frighten Molek or the cub with cameras.

She said keepers checked on mother and cubs this morning but didn't want to get too close.

"She was like: Err, what are you doing here? They will gauge when it is safe," Ms Healy said.

She said keepers were being extra cautious and did not want to put undue pressure on Molek.

"She could roll over on to one of them or do something that is not in the best interests of the cubs," Ms Healy said.

A naming competition, with proceeds going to conservation would be held over the next month.