Tyler De Martini died Wednesday afternoon surrounded by friends and family at Highland Hospital in Oakland.
Friends, many of whom packed the hospital to offer support and prayers to the critically injured Berkeley teenager, said doctors determined earlier in the day that De Martini was brain dead.
His family took him off life support just after 4 p.m.
De Martini, 18, was struck by a car Monday night while riding his skateboard on Marin Avenue.
Friend Gabe Scaglione said Tyler was kept alive by machines for much of the day Wednesday, in part to allow loved ones to spend some final moments with him.
Tests for brain activity came back negative on Wednesday morning, said Gabe, a senior at Albany High School.
Those at the hospital have been coming to terms with the loss; the first apparent report of Tyler's pending death was posted online by friend Laila Fawzi, who wrote on Twitter, at about 2 p.m. to Tyler: "I will never forget you.... I love you so much."
Albany mom Amanda Azevedo said her daughter went to Highland Hospital to visit Tyler on Wednesday. Azevedo shared, via a private message on Facebook, that her daughter called her, crying, at about 2:30 p.m., saying Tyler "passed away before they got there."
Highland Hospital spokesman Warren Lyons said, at about 2:50 p.m., that Tyler's official status "remains critical."
Berkeley Police Department Sgt. Mary Kusmiss wrote, via email, that Tyler was "still alive" as of 3:54 p.m.
But friends and family members have been sharing additional information with Patch.
Gabe Scaglione's mom, Janet, said via email that a number of kids were at the hospital writing notes to Tyler to say goodbye.
Azevedo said her daughter went to Highland "with a few close friends; they're all still together. I told her she could be with them for a while, to talk and cry and be together."
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Berkeley Patch interim editor Emily Henry contributed to this report.
[Editor's Note: This story was updated after its initial publication at 3:30 p.m., Feb. 1, following official confirmation of Tyler De Martini's death.]