Allan McNish
BBC Radio 5 live analyst

"Lewis Hamilton has been in deep discussion with the engineers. The floor is off and the gearbox is now off. They don't know exactly what the problem is but they are investigating. There is no way he will be back out in this session."

Image source, Lewis Hamilton

Lewis Hamilton has little more to do than twiddle his thumbs in the Mercedes garage as work continues on his car, so instead he has taken to tweeting this picture and the caption:, external "I had a special helmet made to celebrate Petronas & Malaysia. Due to the FIA's new rule, I can't wear it."

Andrew Benson
Chief F1 writer in Sepang

"For those looking for a chink of light at the end of the long, dark tunnel in which McLaren find themselves, Jenson Button offered it, predicting a step forward this weekend. Of sorts, anyway.

"'If you look at it from afar, you probably won't see any changes,' Button said, 'but if you look at the lap times compared to other people, I think you will see a change. The problem is that we are so far behind that you won't see a position change. There will be a good chunk in terms of performance and it comes from the power unit and in terms of cooling but also in terms of aerodynamics as we have got some new parts on the car, which will help. You could get the snowball effect where suddenly you find more time than you expect because things start working and fall into place, which is exactly what I'm hoping happens.'"

Sebastian Vettel is up to third fastest with 1:41.471, while Nico Rosberg continues to lead the way.

Meanwhile, Jenson Button - who finished 11th of 11 in Australia - has the 16th fastest time in first practice so far with a 1:43.100.

Daniil Kvyat had a torrid time in Australia as he had to retire on the formation lap and it looks like there may still be gremlins in his Red Bull. Moments after reporting a loss of power at Turn 5, he then says over team radio there "something strange going on with the brakes and the power".

Sebastian Vettel is on a flyer, and his first run sees him go sixth fastest with 1:42.137.

There's a moment for Felipe Massa as he runs deep into the corner at Turn 11 and is briefly on to the grass, but he recovers and gets back on his way.

Lee McKenzie
BBC F1 pit-lane reporter in Sepang

"I am just outside Lewis Hamilton's garage and there is a lot of work going on with the car. They are putting the bodywork on at the moment but it looks a little more serious than just stopping out on track. They have just taken the floor off."

Image source, Formula 1

Formula 1: How do you keep cool when the track temperature is 44C? Dry ice, if you're Dany Kvyat.

Andrew Benson
Chief F1 writer in Sepang

"Lotus's Romain Grosjean is confident of a strong performance this weekend, despite his retirement on lap one in Australia. The mood at Lotus is positive this season and Grosjean says he believes there was enough evidence in Australia to mean the team should 'look forward not back'."

Romain Grosjean, who retired on the first lap in Australia, is up to second in the Lotus with a 1:41.543, just under a second slower than Nico Rosberg's best.

We're still waiting for Sebastian Vettel to clock a timed lap for Ferrari, but he is out on to the circuit now.

Andrew Benson
Chief F1 writer in Sepang

"I've been out watching on track this morning and a couple of things were very noticeable. One was just how much all the drivers were struggling getting the cars slowed down for the Turn Nine hairpin, with the energy recovery systems in full 'harvest' mode and a tailwind pushing the cars on. Nearly everyone had a 'moment' going in, locking up or running wide.

"The other issue was just how little running the teams were doing. The reduction of permitted engines to just four this season is not doing the show any favours. On the sort of bright side, there are only a handful of spectators here to see the non-action."

Fernando Alonso locks up going into Turn One, prompting him to complete a particularly cagey-looking lap. A much better take of the first corner on his next run and he is pushing a bit harder now.

Will Stevens improves with a 1:47.734. It is not enough to lift him off the bottom of the timesheet but encouraging stuff for Manor as Stevens is told "everything is looking good" over team radio.

Will Stevens takes advantage of the clear circuit to post a 1:51.091, over 10 seconds slower than Nico Rosberg's pacesetting time, but nevertheless a welcome first flying lap of 2015 for Manor.

Manor's Will Stevens is the first to remerge on the circuit after that spell of silence, with 45 minutes of the session remaining.

Allan McNish
BBC Radio 5 live analyst

"With it being a race engine and those being in limited number it is better to be safe than sorry. Right now, Lewis has done four laps but they were all in and out laps, a sort of 'get to know you' with the circuit and him."

Lewis Hamilton: "There's a click in the rear - and the gears still worked, but I stopped the car like you told me to. I would have made it back." Race engineer: "We have no telemetry so we didn't want to risk the engine."

Image source, Thanyapuraphuket

While the teams that struggled with technical gremlins in Australia will be working hard to get things right in Malaysia, the drivers have their own issues to contend with - namely the heat.

The Malaysian Grand Prix is one of the most physically demanding races on the calendar, with temperatures inside the cockpit capable of exceeding 50 degrees Centigrade.

From playing tennis to sitting in a sauna, all the drivers have their own ways of acclimatising. Here's Jenson Button at a heat training camp in Phuket, Thailand, earlier this week.

Before Lewis Hamilton came to a stop, Fernando Alonso recorded his first timed lap in a practice session this year, a 1:45.101 which is the slowest of the 16 times posted so far.

Team garages are a hive of activity at the moment, with the circuit empty.