Investigators say the incident happened on the Route 99 bus on Route 202 at Mall Boulevard around 8 p.m. Thursday.
Officers first responded to the scene for a reported stabbing. Several 911 calls indicated that multiple people may have been stabbed after an altercation on the bus as it traveled past the Macy's store, according to police.
When Upper Merion police arrived at the scene, they found three juveniles suffering from lacerations from a knife.
A fourth person with lacerations on her hands was found a short time later, police say. Officers say they found her near the rear of a business located on Allendale Road.
The fight was reportedly between three sisters -- ages 8, 15, and 16 -- and a woman in her 30s. It began over a seat on the bus, according to police.
The argument escalated when one of the juveniles allegedly threw a drink at the adult woman.
"The three juvenile females charged the adult female, knocking her down on the bus during the course of the altercation. That's when the adult produced a short, small pocket knife," noted Lt. Declan Coyle with Upper Merion police.
At one point during the altercation, officers say passengers and the bus driver split up the fight, and those involved left the scene.
"We had four total victims, came in as a stabbing but they're more lacerations, superficial wounds," Coyle said. "We're trying to determine if this is an issue of self-defense or mutual combatants. We're trying to determine who is the aggressor at this point."
All four of them were transported to nearby hospitals with non-life-threatening injuries. They were all treated and discharged, police say.
No charges have been filed at this point, according to authorities.
Anyone who may have witnessed the incident is asked to contact the police at 610-265-3232.
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