Emergency personnel were using ladders to retrieve people stranded on a monorail at the Dallas Zoo.
Dallas Fire-Rescue spokesman Jason Evans says the monorail stalled, stranding about 50 passengers visiting the zoo.
There were no reports of injuries.
The aging monorail has a history of malfunctioning. Nearly 100 people were stranded when it stalled in February.
Monorail Safari stopped today after an off-zoo power surge. Our amazing guests stayed calm & cheery as Dallas Fire helped them down.
— Dallas Zoo (@DallasZoo) August 6, 2014
In recent years it's malfunctioned on at least two other occasions, each time requiring emergency workers using ladders to rescue passengers.