A social media-promoted party in Morgan Hill turned deadly Saturday night when a gunman opened fire on a crowd of more than 300 people, killing one and sending six others to the hospital — with no arrests made and the Santa Clara County Sheriff's Office warning the investigation will be "lengthy and complex."

The shooting erupted in an open field near Hale and Miramonte avenues in unincorporated Morgan Hill, an area policed by the Santa Clara County Sheriff's Office rather than the city. Deputies had been called initially for a disturbance — intoxicated people in the street and a bottle-throwing incident — only to arrive and find a mass-casualty scene. The case underscores the dangers of large, unauthorized gatherings organized through social media with no permitting or security infrastructure.

Deputies from the Santa Clara County Sheriff's Office were first dispatched to Hale and Miramonte avenues around 10:15 p.m. Saturday for reports of intoxicated individuals in the street and someone hurling bottles at a vehicle. What they found was far more serious.

More than 300 people were already scattering from the field when deputies arrived, fleeing what the sheriff's office described as a "chaotic scene." Brooks Jarosz, the office's senior communications officer, said deputies heard gunshots and immediately called for backup. First responders located multiple gunshot victims; one person was pronounced dead at the scene.

Six others were transported to area hospitals. Jarosz confirmed that some have since been discharged, but others with serious injuries remain hospitalized. All victims are adults; the sheriff's office has not released names or ages. The agency initially reported eight people shot before correcting the total to seven, including the person killed.

For neighbors close to the open field, the sound of gunfire was at first indistinguishable from the noise of the party itself. "We didn't know it was a gunshot," one Morgan Hill resident told KSBW. "We just thought it was just music. And then people having a loud party over there, and then they might shoot fireworks or something like that."

The party had been promoted on social media as a "birthday bash." The sheriff's office characterized it as an "unsanctioned party promoted through social media," held in an open field. Per the sheriff's office, a designated area was established nearby so attendees could reconnect with one another.

Preliminary information indicates a handgun was used. No arrests have been announced. Crime scene investigators and K-9 units worked through the night and into Sunday, searching for shell casings and other physical evidence.

Sheriff Robert Jonsen issued a statement condemning the violence: "This tragic and senseless violence is entirely unacceptable. Our hearts go out to the victim's family, those recovering from their injuries and everyone in our community affected by this traumatic event. We will work tirelessly until those responsible for this horrific act are identified, apprehended, and held fully accountable."

The Morgan Hill Police Department, Gilroy Police Department, San Jose Police Department, and California Highway Patrol all responded to assist with first aid, scene security, traffic control, and investigative support — a multi-agency response reflecting the scale of the scene.

Anyone with information is urged to contact the Santa Clara County Sheriff's Office.