Marussia driver Jules Bianchi has suffered a "severe" head injury in a crash at the Japanese Grand Prix.
The FIA said the Frenchman is in surgery and will be moved to intensive care afterwards.
Bianchi, 25, was unconscious as he was taken to hospital following the incident which brought the rain-affected race to an early conclusion.
He lost control at the same spot on the Suzuka circuit where recovery vehicles were attending a previous crash.
In wet conditions, Sauber driver Adrian Sutil firstly spun and hit the tyre barrier as rain intensified in the latter stages of the race.
While recovery vehicles were lifting Sutil's car, the FIA said Bianchi "lost control of his car, travelled across the run-off area and hit the back of the tractor."
The race was red-flagged and then declared over after 44 laps.
"The driver was removed from the car, taken to the circuit medical centre and then by ambulance to Mie General Hospital," the FIA added in a statement.
"The CT scan shows that he has suffered a severe head injury and he is currently undergoing surgery. Following this he will be moved to intensive care where he will be monitored."
Mercedes driver Lewis Hamilton won the race ahead of team-mate Nico Rosberg, but said: "It is obviously a real anticlimax to hear one of our colleagues is seriously injured. That is the main worry."
Sutil said: "I had aquaplaning in Turn Eight. The rain was increasing and the tyres were going down, the light was going down. It was hard to see.
"I was following Jules very close and had a spin and hit the wall. I was OK and then one lap later, under waved yellows, Jules was in the same trouble."
The race had earlier started under safety car conditions after a heavy downpour on Sunday morning as storms that preceded the approaching typhoon Phanfone hit Suzuka.
It was red-flagged after only two laps because of the weather, before resuming around 20 minutes later under the safety car. After a further eight laps, conditions were deemed suitable enough for racing to get under way.
Despite the conditions three-time world champion Niki Lauda, who was seriously injured in a crash at the German Grand Prix in 1976, felt the conditions were not bad enough to warrant the race being called off.
"The rain was not the real issue," the Mercedes non-executive chairman said.
"There were safety cars put in and the race was run safe more or less to the end, so it could have been run to the end without the accident.
"I don't think the darkness was an issue here. Motor racing is dangerous. We get used to it if nothing happens and then suddenly we are all surprised.
"We always have to be aware that motor racing is very dangerous and this accident is a coming together of various difficult things. One car goes off, the truck comes out and the next car goes off. This was very unfortunate."
Crew members of Marussia driver Jules Bianchi push his car to the grid before the start of the race
Medics at the scene treat Bianchi
The ambulance takes Bianchi from the scene