A takahē has laid an egg at Pukaha Mt Bruce National Wildlife Centre.

After more than 20 years of no takahē laying eggs at a lower North Island wildlife centre, staff were greeted with a surprise.

A ranger at Pukaha Mt Bruce National Wildlife Centre found the mother, believed to be past breeding age, sitting on an egg on Saturday.

Takahē are endangered native birds with a population of 347, including 100 breeding pairs.

SUPPLIED Takahē are endangered native birds with a population of 347.

Despite Pukaha staff assuming 13-year-old Fomi would not have any more offspring, they are hoping the egg will produce a chick.

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Fomi was moved to the centre from Mana Island in June after the centre's male lost its mate.

Takahē thrive in pairs but it was assumed Fomi and Natural, 18, would no longer breed.

But ranger Tara Swan's discovery has staff hoping a takahē will hatch in the next 30 days.

A wildlife centre spokeswoman said there was a high chance the egg was infertile but the team were keeping a close eye on developments.

"The two birds hit it off from the moment they were introduced and Pukaha rangers have witnessed the pair breeding."

If the egg is fertile, it will be the first takahē chick hatched at the centre in two decades.

Department of Conservation senior takahē ranger Glen Greaves said takahē had experienced the highest annual growth rate in almost 70 years.

The number of breeding pairs also more than doubled in 10 years to 100, Greaves said.