One person was shot in the 1000 block of Franklin Street late Monday night, according to city police.
"I got a lot of blood here, expedite the ambulance," one officer at the scene told a dispatcher.
One neighbor said there was a white man "riddled with bullets" laying unconscious on the ground.
Within minutes, officers had one person in custody and had recovered the handgun believed to have been used in the shooting.
Officers rushed to the area of 1014 and 1018 Franklin St. about 10:30 p.m. to investigate a report of five shots fired. As they approached the scene, they found one person "down on the ground," according to reports.
It was unknown if the shooting took place inside a home or in a yard.
There were unconfirmed reports that there had been two or more people fighting.
"I need two agents be sent here," an officer was heard telling a dispatcher, referring to full-time criminal investigators.
"We need additional units (police officers), mutual aid, until things settle down here," a patrol supervisor at the scene was heard telling a dispatcher.
Officers from other departments rushed to help.
An ambulance rushed the gunshot victim to the Williamsport Regional Medical Center.
No information was provided on the genders or ages of the victim or the suspect.
This is the second shooting in the city in as many days. A man was critically shot on his front porch, allegedly by his estranged wife, in the 1100 block of Memorial Avenue about 10:10 a.m. Sunday. He is recovering at a trauma center while the woman is in the Lycoming County Prison on attempted homicide-related charges.
At Monday night's scene, officers moved quickly to cordon off much of the area with tape in an effort preserve evidence.
Neighbors said they heard three to four "extremely loud" gunshots. An elderly lady said she was so frightened and shook up because she heard the gunfire over the loud volume of her television set.
Neighbors also reported hearing arguing outside moments before the gunshots erupted.
A second ambulance was needed at the scene to transport a man, whose injuries were not known. However, a reporter noticed the patient was handcuffed behind his back as he was placed on a litter. A police officer climbed in the back of the ambulance before it left for the hospital.
Police Chief Gregory Foresman arrived on the scene, but he said it was too early for any information to be released.