Russian GP practice halted after Sainz crash

"Is he OK? Because it looks like a big one," said Toro Rosso team mate Max Verstappen over the team radio as the medical car attended the scene of the impact at Turn 13.

"We lost the power on the car, we don't know," came the reply.

In a further indication of the severity of the accident, race officials said the session -- which had 25 minutes remaining at the time of the red flag -- would not be restarted.

Television images showed Sainz's car had penetrated deeply into the TechPro barriers, which are designed to absorb energy, in what appeared to be a very high speed impact. There were no television replays of the crash.