Ahead of today's opening session, the air temperature is 29 degrees C, while the track temperature is 37 degrees.

Tyres available this weekend are the hard (prime) and medium (option). There are two DRS zones, one on the start/finish straight and the other on the final straight.

The big talking point this weekend is the return of Fernando Alonso, whose comments during yesterday's press conference posed more questions than answers in reference to his crash during pre-season testing.

This weekend also sees the return of Valtteri Bottas following his back problem in Melbourne and, hopefully, Manor following its no-show down under.

Having achieved a 1-2 here last year, and again two weeks ago, Mercedes is the red hot favourite here, however, Ferrari is confident than it can match its Melbourne pace here, this being a 'traditional' circuit.

While Sauber is looking to build on its Melbourne performance, and Williams keen to benefit from having both cars in action, all eyes are on Red Bull as its relationship with Renault worsens.

The only reserve driver on duty today is at Sauber where Raffaele Marciello replaces Melbourne star Felipe Nasr.

The lights go green and Ericsson leads the way, followed by a whole host of others including Vettel and Massa. Stevens, in the Manor, is another early riser as is Alonso.

Within the first five minutes all but Merhi and Bottas have made an appearance.

As he begins a run of four timed laps, Hamilton is told that he has no telemetry. He returns to the pits.

Sensors abound, some teams running the 'garden fence' variety witnessed pre-season.

Merhi is last out but immediately runs into problems, the car slowing and crawling its way back to the pits. He first reports problems with braking before adding he has lost power also.

Ericsson posts the first time of the weekend, the Swede stopping the clock at 1:44.483. Elsewhere, Bottas heads down the pitlane.

Verstappen posts a 42.725 and Massa 43.029 as Rosberg runs wide at T9.

Despite running wide, Bottas raises the bar with a 42.533 only to be beaten by Raikkonen and then Grosjean (42.202).

Oh dear, Rosberg gets serious with a 40.973, 1.229s quicker than Grosjean's best.

As Ricciardo goes third (42.226), Verstappen is told that he has a puncture and must abandon his run and head to the pits.

A big lock up for Raikkonen in T15 who subsequently runs wide. Rosberg improves to 40.561.

Approaching the end of the opening half-hour, all but Vettel, Stevens, Hamilton and Merhi have posted times. Indeed, Hamilton has stopped on track at T9 and is pushed to safety by the marshals. He climbs from the car.

As the circuit falls quiet, and the teams hand back one set of prime tyres, it's: Rosberg, Sainz, Raikkonen, Grosjean, Ricciardo, Massa, Ericsson, Kvyat, Bottas and Maldonado.

Hamilton says he could have got back to the pits but his team instructed him to stop on track.

There follows more than ten minutes of total inactivity. Some of it, admittedly, while Hamilton's car is rescued, but much of it with an eye on the four power unit rule and the need to save components.

Finally an engine fires up, and moments later Stevens heads down the pitlane. As he begins his first flying lap, the red and white car doesn't appear to bear a single sponsor logo, not even (team owner's company) Ovo Energy.

His first flying lap sees Stevens post 51.091, over 10s off the pace. Next time around he improves to 47.734s.

As Button seeks to improve on 44.395, Alonso prepares to go out in the second McLaren.

Stevens now up to 46.686, 6.125s off the pace.

A mistake by Alonso in T1 as he locks-up and misses the apex. He subsequently crosses the line at 55.313.

Grosjean improves to second with a 41.543, with Rosberg raising the bar ever higher moments later with a 40.124.