A woman opened fire at YouTube’s California headquarters during lunchtime on Tuesday — wounding at least three, including her boyfriend, before killing herself, according to reports.

The shooting appeared to stem from a domestic dispute, with law enforcement sources telling multiple media outlets in San Bruno that the suspect’s partner was the intended target.

Police officials said the woman — who had not yet been named by publication time — acted alone, describing the scene inside the headquarters as a “pretty hectic scenario.”

Armed with a pistol, the woman approached an outdoor dining area and blasted away at her boyfriend around 12:45 p.m. local time, sources told local TV affiliates KRON4 and KTVU.

She shot him and two others — and then killed herself, according to police.

The victims were rushed to Zuckerberg San Francisco General Hospital in serious, fair and critical condition. They were described as two women — ages 32 and 27 — and a 36-year-old man.

Hospital officials said they were all shot more than once in the chest and other extremities.

The midday shooting sent hundreds of workers into a panic and sparked a massive police response.

“Active shooter at YouTube HQ,” employee Vadim Lavrusik tweeted. “Heard shots and saw people running while at my desk. Now barricaded inside a room with coworkers.”

YouTube product manager Todd Sherman said he was sitting in a meeting when he heard the commotion.

“We heard people running because it was rumbling the floor,” he tweeted. “First thought was earthquake.”

As Sherman tried to escape, he “looked down and saw blood drips on the floor and stairs.”

“Peaked around for threats and then we headed downstairs and out the front,” he added.

Photos and video posted on social media showed YouTube employees walking out of the company’s headquarters with their arms raised. Several ambulances were on the scene and cops were advising people to stay away.

At least one witness told KRON4 that they heard 20 shots fired before police responded.

YouTube’s parent company, Google, released a statement on Twitter about the active-shooter situation, but didn’t provide any specific details.

“We are coordinating with authorities and will provide official information here from Google and YouTube as it becomes available,” the company said.

YouTube employees reportedly took shelter anywhere they could after being evacuated Tuesday, with some hunkering down in restaurants and cafes.

“They came in from a back door,” recalled Michelle Tam, a hostess at the nearby Hashes & Brews restaurant who spoke to the LA Times.

“They sat down at a table.They were in a daze,” she said, noting how one of the employees had a partial bullet fragment in her shoe. “One guy, there was a little blood on his head.