@JamesDuncan: In terms of detail, the Mercedes and Ferrari look more advanced. Red Bull appear to have done a very good job with the packaging, as has McLaren. However, more updates will come next week for all four teams and even more in time for Melbourne.
@DarrenTaylor: No. But it's not unusual for meetings to take place in the paddock between team bosses.
@Skejck: Next week is the plan.
Red flag. Alonso's McLaren has stopped on track.
He'd just set a slightly improved time, but has now stopped the running. Not good for McLaren at this stage of the day.
@DarrenTaylor: They rarely are happy with Renualt! They have been quite open in saying that they will still be down on power this year. They were 10% down on the Mercedes last year - which is somewhere in the region of 75-80bhp. Closing that gap is crucial, but it's still going to be a big deficit. As a result the team has to take risks with the aero and packaging to make up the difference and that can result in reliability issues.
The McLaren stopped at Turn 4, but hard to say what the problem was at the moment.
Nate's watching trackside at the moment and says Alonso has stopped alongside the inside wall at Turn 4. That'll most likely be the end of his testing week as he's handing over to Button at lunch.
The latest images from the circuit show an the circuit's medical vehicle between Turns 3 and 4. Hopefully that's just a precaution, but does suggest it was an accident and not a reliability problem.
The chequered flags are out for an early end to the morning session. We'll bring you updates on Alonso as we get them from the track.
So it was an accident for Alonso on the run down to Turn 4, possibly losing the rear on the exit of Turn 3 like Maldonado did last year. Most likely he was taken to the medical centre by the ambulance as a precaution judging by the tweet from the circuit.
So we now have an hour's lunchbreak at the Circuit de Catalunya. We will, however, bring you any updates on what happened to Alonso at Turn 4.
The medical helicopter has just taken off from the circuit, Alonso is on board and being taken to hospital for precautionary checks.
I can tell you that the impact does not look serious and the reports coming in are that he's being taken away for precautionary checks.
We will of course bring you any further updates on Alonso's condition as and when we get them. After the accident he was reported to be okay and conscious, so it appears he has been taken to hospital for precautionary checks.
Track action is set to resume any moment now. There was a bit of a delay, but of course we can't have testing without a medical helicopter in place.
Rosberg and Kvyat are the first to to return to the track after an extended lunch break for everyone.
@AnthonyDadley: Ricciardo won three races with a car that was a firm second to Mercedes last year. I think he's capable of five or more in a season alone with a good car. Kvyat shouldn't be underrated but it's fair to say he still has to prove himself. Sainz and Verstappen are both young, but Sainz comes to F1 as the Formula Renault 3.5 and you can't ask for a much better credential than that. Verstappen is an unknown, but Red Bull has a lot of faith in him and historically that is a good sign.
@Rodster: The front wing was missing, but it's an odd one because it doesn't seem like that heavy an impact.
For those asking, this is all the information we have on Alonso at the moment. No news on whether the car will return to the track at the moment, but we will bring you more news when we have it.
Vettel, Grosjean, Kvyat, Rosberg and Bottas are all on track at the moment.
@Adam: The Sauber stopped in the pit lane earlier today. No news from the team, but my guess would be an engine change.
Just as I typed that last post, Nasr hits the track in the Sauber for a single lap.
@McLaren: That McLaren tweet was from about 30 minutes ago, but good news on Alonso's condition nonetheless.