Top Gear presenter Richard Hammond has suffered a "significant brain injury" after crashing a jet-powered car at speeds of up to 300mph during filming.
Richard Hammond is seriously ill in a Leeds hospital
Doctors at Leeds General Infirmary said they were "reasonably optimistic" the 36-year-old would make a good recovery.
The BBC, which is likely to face close scrutiny, has begun an inquiry. The police and the Health and Safety Executive (HSE) are also investigating.
Event organisers insisted that proper safety precautions were taken.
Hammond's wife Mindy was at his bedside in the Leeds hospital and he was also visited by Top Gear co-hosts Jeremy Clarkson and James May.
Referring to Hammond by his nickname, Clarkson said in statement: "Both James and I are looking forward to getting our 'hamster' back."
The presenter had been driving a jet-powered dragster similar to the Vampire - used by Colin Fallows to set the British land speed record of 300.3mph.
Primetime Land Speed Engineering, which is jointly run by Fallows, organised the event.
A spokesman for the firm said the vehicle Hammond was driving "had been prepared and was being operated to the highest of standards".
Keith King, an inspector for the HSE, said it was a "very unusual case", adding that the executive would look at the preparation and planning of the event and contingencies for an emergency.
Meanwhile, Supt Martin Deacon of North Yorkshire police, said his officers would initially focus on the road and the vehicle.
On Thursday afternoon, the dragster was lifted on to the back of a lorry and taken away for forensic examination at an undisclosed location.
The BBC said in a statement that it had begun an investigation into the accident and promised full co-operation with the HSE.
"We continue to be concerned about [Hammond's] condition and we are keeping in touch with his family," the statement said.
Top Gear has courted controversy in the past over its big-budget car stunts, and in 1999 a group of MPs criticised the series for being "obsessed with acceleration and speed".
Last year, lobby group Transport 2000 called for the show to be taken off the air accusing it of "glamorising speed and failing to make the connection with danger on the roads".
At the time, Hammond defended the programme, saying: "Top Gear is an entertaining show, for people that are interested in cars, that is driven by people who have been motoring journalists for many, many years."
Hammond had to be cut free from the car on Wednesday evening after eyewitnesses at the Elvington airfield near York described how he "veered off to the right" and the car's parachutes were deployed.
A website set up for well-wishers to make donations to the Yorkshire Air Ambulance, which airlifted Hammond to hospital, has so far raised more than £4,000.