A brother and a sister of crashed French Formula One driver Jules Bianchi were to join their parents at his bedside in a Japanese hospital, a source close to the family said on Thursday.
Tom and Melanie Bianchi were due in Japan late Thursday and expected to visit the Mie General Medical Center in Yokkaichi, where their brother was taken after the horrific smash at the Suzuka Circuit on Sunday.
Lorenz Leclerc, a young man whom Bianchi's supporters described as his best friend, joined his parents at the hospital earlier on Thursday.
Bianchi, 25, was knocked unconscious in a high-speed crash into a recovery vehicle during Sunday's rain-sodden Japanese Grand Prix at Suzuka.
The Frenchman underwent emergency brain surgery, with doctors saying he was in critical but stable condition.
It could be weeks before doctors know how badly damaged Bianchi's brain is, a specialist warned.
Motor racing's governing body the FIA said Wednesday it had ordered a report into the crash to be supervised by its top race director.
FIA president Jean Todt has asked Charlie Whiting, the Formula One race director, "to carry out a report on the precise circumstances which led to the accident", the federation said in a statement sent to AFP.
Bianchi suffers a diffuse axonal injury -- trauma that is spread across the brain rather than in one place -- caused by the shockwave from the sudden impact of the crash travelling through the brain. This causes bruising and kills cells.
The body's response to the injury -- swelling -- exacerbates the problem because it restricts blood flow to the brain, causing more damage.
Experts say recovery rates from this kind of injury, which is frequently caused by vehicle crashes, are not encouraging.