Authorities say a second boy has died after his family's car plunged into Los Angeles harbor, killing his 13-year-old brother. The family had left a waterfront restaurant Thursday night when their sedan ran off the road alongside a working dock at the Port of Los Angeles, landing upside down in about 30 feet of water. The boy's parents swam to the surface, but the children were stuck in vehicle. They weren't breathing when rescuers brought them up. The teen died at the hospital several hours later. Coroner investigator Joseph Cronin tells City News Service that the eight-year-old boy died Friday afternoon. Scroll down for video . Pulled from the water: A car plunged off a road into Los Angeles harbor on Thursday, and two children pulled from the submerged vehicle were hospitalized in grave condition. Both have now died . Rescue attempt: The two children pulled from the submerged vehicle by firefighters were hospitalized in grave condition, authorities said . Hero: Firefighter Miguel Meza (left) who dove into the water in San Pedro after a car carrying a family of four plunged into the water has been hailed a hero on the Facebook of City Councilman Joe Buscaino (right) The car left a parking lot at the Ports O' Call entertainment area of San Pedro shortly after 6pm and ran off the road at Berth 73 of the Port of Los Angeles. The car traveled some distance before lurching into the harbor, where it landed upside down in about 30 feet of water just off of Berth 73, Fire Department spokesman Brian Humphrey said. 'They looked like they were doing about 30 mph and turned right off the wharf, right into the water,' said fisherman Ray Prince, 33. 'The car just sunk.' The man came up first and swam quickly to a ladder out of the water, Prince said. 'The poor lady was screaming hysterically. Just screaming. I thought she was going to drown,' he said. The adults were described as being in fair condition but 'clearly emotionally distraught'. Firefighter Miguel Meza, who dove into the water, has been hailed a hero on the Facebook page of Los Angeles City Councilman Joe Buscaino. 'Firefighter Miguel Meza jumped into the water at Berth 73 tonight in San Pedro after a car with a family of four drove into the water. This man is a true hero in the City of Angels and I am so proud of him!, he said. Sucessful search: Divers emerge from the water as debris believed to be from the car floats to the surface where a car went off the berth and into the water . Divers working in murky water searched the car and even opened the trunk, but they found no one else in it, Humphrey said. The cause of the accident was under investigation. 'We don't know at this time whether it was an accident or an intentional event,' Humphrey said. Nearly 100 firefighters, divers and helicopter and boat crews went to the scene, Humphrey said. ABC reports that the event that led up the incident remain unknown. Witnesses told police that they heard screeching tires before the car made the plunge. Two dead: One of the children who fell into the LA Harbor died Thursday, while a second was confirmed as dead on Friday .
Car plunged off a road into Los Angeles harbor on Thursday .
The parents swam to the surface but the two boys were trapped .
Both died were pronounced dead in hospital .
The adults are in a fair condition .
Police are investigating whether the crash was intentional .
The victims have not been identified .
Firefighter Miguel Meza who dove into the water has been hailed a hero .