A teenage marathon runner is in critical condition after falling nine stories from a Gold Coast apartment building.

Tyler Calleja, 18, was found in the car park of the Essentia Building in Surfers Paradise around 4:30 a.m. on Sunday. Paramedics treated him at the scene for serious head and abdominal injuries before he was transported to Gold Coast University Hospital. He remains in intensive care with severe brain trauma.

Investigators believe Calleja had returned to the apartment complex after completing a half-marathon earlier that day. According to reports, he misplaced his room key and attempted to gain access to his apartment by climbing a fence, accessing a fire escape, reaching the roof, and then trying to descend to his unit. He fell into the car park area, landing on a vehicle.

Earlier on Saturday, Calleja had posted on social media about his successful half-marathon, noting he achieved a personal best time, beating his previous record by 13 minutes. He also recently completed a 100km run in 24 hours to raise funds for the Queensland Children's Hospital.

The 18-year-old had completed a half-marathon just hours before the horrific incident.

Calleja fell from the Essentia building in Surfers Paradise and was found at about 4.30am on Sunday after landing on a vehicle in the car park.