The heartbreaking way one dad found out his son had died in the California mass shooting.

Jason Coffman was woken up by his son’s friends banging on his door just before 1am.

They had terrible news: There had been a mass shooting at Thousand Oaks’ Borderline Bar and Grill in Thousand Oaks, which is about 64km west of Los Angeles.

He knew his 22-year-old son Cody Coffman was there and fearing the worst, he tracked Cody’s phone.

“It’s there [at Borderline],” Mr Coffman told CNN. “It’s not moving, that’s the problem.”

Hours later, Cody was identified as one of the 12 victims who died when a gunman opened fire inside the club that had been hosting a college night.

With his nightmare confirmed, Coffman sobbed.

“They found him,” he told reporters.

“Oh Cody, I love you son. This is a heart I will never get back. I cannot believe that it’s happened in my family.”

“I can not believe it’s happened to my family,” says Jason Coffman, father of California shooting victim Cody Coffman. “I’m speechless and heartbroken…. My life has changed now forever” https://t.co/HVITJqO5xN pic.twitter.com/MPIZONA7O3

— CNN Newsroom (@CNNnewsroom) November 8, 2018

Before Cody was confirmed dead, Coffman has spent the night frantically driving to hospitals in the region trying to find information.

Eventually, he was told to wait at a teen centre with other parents.

Coffman recalled the final conversation he had with his son, who had recently moved in with him.

“This is going to be an absolute heart wrenching time for me and my family,” he said to reporters.

“I talked to him last night before he headed out the door. The first thing I said was ‘please don’t drink and drive.’ The last thing I said was ‘Son, I love you’.”

He said Cody had headed to the bar with a few of his female friends.

“Some of his girlfriends got out but they didn’t know where Cody was, I’m sure he was there helping, shielding anybody that he could.”

The shooting also claimed the lives of 11 others, including 23-year-old Justin Meek, Alaina Housley, the 18-year old niece of actress Tamera Mowry-Housley and Sergeant Ron Helus, a 54-year veteran of the police force who had planned on retiring soon.

Our thoughts are with the family and friends of Sergeant Ron Helus and all the victims of last night’s tragedy in Thousand Oaks. We are deeply saddened by this event in our county. pic.twitter.com/i9YwtMImLp

— Ventura Police (@Ventura_PD) November 8, 2018

Police say the shooting began on Wednesday at 11.20pm local time (6.20pm AEDT) at the Borderline Bar and Grill in Thousand Oaks, which is about 64km west of Los Angeles.

The gunman was found dead at the scene. Ventura County Sheriff Geoff Dean named the suspect as Ian Long, 28, who likely took his own life.

It was the third mass shooting in the US in under two weeks, six days after the death of two women at a yoga class in Tallahassee, Florida, and 12 days after a gunman killed 11 worshippers at a synagogue in Pittsburgh.