The victims were a Pleasanton family of two adults and two children under the age of 15.
Police continue to investigate a single-vehicle accident that occurred around 9 p.m.
The coroner's office is still working to notify the next of kin, so the family's identity has not yet been confirmed.
A full investigation of the accident is ongoing, although police say speed may have been a factor. The car appears to have lost control and collided with a large oak tree, killing all four family members inside.
RELATED: Family of 4, including 2 kids, killed in Pleasanton crash on Foothill Road, police say
This is a breaking news update. See our previous coverage below:
Pleasanton police said a crash Wednesday night killed a family of four, including two children.
Police said Thursday morning that one car was involved in the crash, which happened around 9 p.m. on Foothill Road near Stoneridge Drive. The road was closed until 7:20 a.m. Thursday.
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The family has not yet been identified as police as still notifying next of kin, but police say they believe the two children killed were in elementary and middle school.
Police say they are unsure if speed was a factor in the crash, and don't know if any alcohol was involved. Foul play is not suspected.
The family's electric car reportedly caught fire after the crash and reignited a few times while investigators were clearing the scene.
"We are conducting a thorough investigation and do not have additional information at this point," police said on social media. "We will release further details as they become available. For now, our priority is protecting the victims' identities as we notify family and complete our investigation."
The Pleasanton Unified School District said that the kids involved were students at their schools.
A district spokesperson talked with ABC7 News moments after he visited one of the school sites.
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"It's somber, I think whenever anything like this happens and it impacts the entire family, it's tragic. I don't know how else to put it," said Patrick Gannon, director of communication with the Pleasanton Unified School District.
The district said it's going to provide extra counseling and support resources through at least Friday.
"We want to do everything that we can to support them and just want to make sure that students know that there are adults that care about them, and that are here for them when and if they need," Gannon said.
Throughout Thursday, loved ones, friends, and strangers payed their respects at the scene.
Hasan Shaikh said he worked with the father at a South Bay tech company.
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"It's very shocking, very nice person - always you know, energetic," Shaikh said.
Shaikh didn't want to identify the family until authorities do.
"It was a great family, great personality they definitely will be missed - great father, great coworker and a great person overall," Shaikh said.