Valtteri Bottas also heads back out in the Williams.

Sebastian Vettel has been speaking about Fernando Alonso's accident. The Ferrari driver was right behind Alonso at the time of the incident, and said: "The speed was slow - maybe 150kph. Then he turned right into the wall. It looked strange."

Green again and Carlos Sainz and Nico Rosberg get straight back on to the circuit.

The Force India is on the back of the recovery truck and you would imagine we will be back under way shortly.

1. Carlos Sainz (Toro Rosso) 1:25.605 (76 laps)

2. Felipe Nasr (Sauber) 1:26.121 (24 laps)

3. Daniil Kvyat (Red Bull) 1:26.179 (58 laps)

4. Sebastian Vettel (Ferrari) 1:26.312 (69 laps)

5. Nico Hulkenberg (Force India) 1:26.591 (36 laps)

6. Nico Rosberg (Mercedes) 1:26.782 (83 laps)

7. Fernando Alonso (McLaren) 1:27.956 (20 laps)

8. Romain Grosjean (Lotus) 1:28.029 (84 laps)

9. Valtteri Bottas (Williams) 1:28.171 (83 laps)

That's the third red flag of the day, and there is apparently smoke coming from the rear of Nico Hulkenberg's VJM07.

Red flag, Nico Hulkenberg coming to a stop at Turn One.

Force India:, external Nico completed his instal lap following some lunchtime checks and changes and is now heading out for his first run proper.

Nico Hulkenberg does indeed depart the Force India garage, but only for a brief foray on to the circuit before returning to the pits.

Valtteri Bottas and Romain Grosjean, meanwhile, are lapping in the 1:30s as they continue their race sims.

Image source, Force India

Force India:, external The number 27 car is ready to depart the number 27 garage.

F1 journalist Dan Knutson in Barcelona: "While they still put the screens up in front of the garage doors, the teams are not being as paranoid as they were about concealing their cars when the driver comes in and they push the car into the garage. By now most visible secrets the cars had at the start of testing are known to rival teams. Plus these are the interim-spec cars that will be obsolete after being updated at the next test with new race-spec parts that will be used in the Australian Grand Prix."

Felipe Nasr is up to 16 laps for the day and his latest trip round the circuit sees him record a 1:26.121 on softs, which moves him up to second, just over half-a-second behind pacesetter Carlos Sainz.

Image source, Lotus

Lotus:, external And back to the track for Romain Grosjean.

Sebastian Vettel and Daniil Kvyat are back in the pits and the circuit is briefly empty, before Valtteri Bottas re-emerges with hard tyres bolted on his Williams.

McLaren have released a statement regarding Fernando Alonso. Here it is in full:

"Today at 12:35 CET, while testing at the Circuit de Catalunya (Barcelona), during the fourth and final day of the current test, Fernando Alonso's McLaren-Honda car left the track at Turn Three, causing the right-hand side of his car to strike the wall.

"Fernando was driven to the circuit's Medical Centre where the circuit's doctors gave him first aid.

"He was conscious and spoke with the doctors.

"However, as per usual procedure in such circumstances, he was then airlifted to hospital where he is undergoing precautionary checks.

"We will issue a further update in due course."

Sebastian Vettel kicks off this run with a 1:30.100 before Red Bull's Daniil Kvyat heads out and a personal best for today on his 50th lap, a 1:26.935, sees him climb into fifth.

Carlos Sainz returns to the pits and switches off his Toro Rosso, meaning that is his running done for a little while. Meanwhile, Sebastian Vettel and Nico Rosberg are out on the circuit.

That leaves three cars on the track, the Toro Rosso of Carlos Sainz, Felipe Nasr's Sauber and Romain Grosjean's Lotus.

Valtteri Bottas is not out long, though, he heads straight back in.

Image source, Williams

Like Romain Grosjean, Williams' schedule for this afternoon involves a race a simulation and Valtteri Bottas pits after completing 16 laps in this programme. He takes on mediums and heads back out.