A black bear who managed to climb out of a Texas zoo exhibit took a dip in a pond with some harbour seals before staffers tranquillized him.

No one was hurt in the incident at the Gladys Porter Zoo in Brownsville.

Zoo spokeswoman Cynthia Galvan said the 220lb male bear, named Oscar, is staying in his sleeping quarters, out of public view, until repairs are made to cracks in the concrete wall of the bear grotto.

Oscar apparently made his way out by digging his claws into cracks in the grotto's concrete wall, Ms Galvan said.

"A zoo visitor witnessed that he was trying to climb the wall, went to report it to one of the zoo employees," she said.

When staff arrived, Oscar was already out.

"He meandered his way through the amphitheatre and into the harbour seals' pool for a dip," Ms Galvan said.

Staff members contained him within 15 minutes at the pool, she said.

The zoo was locked down, with visitors safely moved into buildings, for about 90 minutes. Meanwhile, the zoo's two harbour seals seemed unfazed by the bear, she said.

"From what I understand everyone was just swimming around. They didn't seem bothered by the bear and the bear didn't seem bothered by them," Ms Galvan said.

Staffers waited for Oscar to leave the pool, then eased him through some opened doors, leading to a behind-the-scenes area, before using a dart to tranquillize him.

Oscar was captured in the wild in 2012 and is believed to be aged about four. The zoo's only other black bear is a female who is about two-years-old.