A Friday afternoon swim in a Philadelphia city-owned pool ended with a trip to the hospital for three kids after they were shocked by an electrical current.

Witnesses say about 20 people were splashing around in the O'Connor Pool at 26th and South Streets in the Graduate Hospital section of the city around 1:15 p.m. when the children were hit by the electricity.

A mother, who saw the shocking take place, said a boy was using a metal ladder to climb out of the water when the current went through him. A girl was hurt moments later, she said.

The lifeguard on-duty screamed for everyone to rush out of the water after realizing the danger, witnesses said. They added that the whole ordeal was disturbing.

Firefighters were called to the scene and quickly cut electricity to the pool's lights, pumps and surrounding structures, Philadelphia Fire officials tell NBC10.com.

Philadelphia Fire Executive Chief Peter Crespo said three children, who are all under the age of 13, were taken by ambulance to the Children's Hospital of Philadelphia. They are all listed in stable condition and expected to be fine.

Officials from the Departments of Parks & Recreation and Licenses & Inspections and PECO Energy were called to the scene to find the source of the electricity. PECO crews could be seen testing the water with the pool's filtration system turned on.

Susan Slawson, First Deputy Commissioner of Parks & Recreation, said work was also being done to a motor nearby, but that the cause remains unknown.

"The pool will be closed until we figure out exactly what has happened here," Slawson said.

Crews were draining the pool to try and find the source.

The incident remains under investigation.