Welcome to coverage of the first practice session of the Malaysian Grand Prix. Reports from the track say its cloudy with a chance of thunderstorms later, although the worst of the weather is in store for Saturday and Sunday.

The teams have been out getting a bit of pit stop practice under their belts this morning. It's already quite hot and humid so it's good practice ahead of the pressure of the real thing on Sunday during the race.

Karthikeyan has been tweeting this morning: "Off to Sepang this morning keeping my fingers crossed for two good and complete practice sessions!"

HRT are hoping to get as much mileage as possible today to give themselves a chance of qualifying on Saturday.

Valsecchi is driving the Lotus this morning in place of Kovalainen, Ricciardo is in for Buemi and Hulkenberg is in for di Resta at Force India.

The session is underway. Trulli hits the track first.

Pirelli has brought an experimental tyre compound to this session, so most drivers will be out on that first while the track rubbers in. We understand it is a super-hard compound as tested at Istanbul last weekend by Pedro de la Rosa.

Karthikeyan and Liuzzi are out on track in the HRTs. Good news for those two.

The drivers on circuit will just be completing an installation lap to make sure the car is working as expected. We're still waiting on Button and Schumacher to hit the track.

Schumacher and Button are with us on track now so all the cars have put in an installation lap.

Ferrari says: "Everything is ok with the cars. Now the programme is to do several runs to check different aerodynamic configurations in order to understand better the behaviour of the 150° Italia. Then we will switch to a more classical Friday programme."

Presumably a "classical" Friday programme is long runs...

Ferrari have also mounted a rather large camera to the front of Massa's car - it won't be a permanent addition.

Hulkenberg is out on the develoment tyres which appear to have no markings on the sidewalls. Most drivers will use those first to save the regular compounds for later in the day.

And Hulkenberg sets the first time fo the morning with a 1:44.557. We're expecting to see times in the mid-to-low 1:30s once the drivers crack out a set of soft tyres this afternoon.

The HRT is running its new front wing as expected but Karthikeyan has pulled over with an apparent engine problem. It belched out a huge amount of smoke almost as soon as he left the garage.

Hulkenberg has set a new fastest time with a 1:41.547. Heidfeld is second fastest with a 1:42.285.

HRT says: "Problems with the Narain's car. We will check whats happen after P1"

I could have told you that.

Heidfeld clocks a 1:40.525 and then his front right brake locks up and remains locked as he goes around the first few corners. Clearly a failure of some sort and he is limping back to the pits. He should make it back but the tyre has gone flat and the bottom of the car is being scraped along the circuit.

Heidfeld is out of the car, he'll be hoping the team can solve that issue as soon as possible and put him back out on track before the end of the session.

Meanwhile, Maldonado has set the second fastest time with a 1:40.854, 0.329 off Heidfeld, and is going quicker on his current lap.

Liuzzi has completed six laps so far in the HRT. So he's already increased the mileage on his car this season by 50%.

Ferrari says: "Fernando left the garage again for another run, once again aimed to collect aero data."

HRT adds: "We are waiting to have the Narain's car back to the garage, but it seems to be a problem related to the engine."

Vettel sets his first lap of the weekend to go tenth fastest with a 1:42.901.

Both Mercedes are on track and lapping in the high 1:40s and low 1:41s. Its a crucial weekend for the team after a disappointing performance and double retirement in Australia.

Webber has set a new fastest time with a 1:39.870.

HRT has retrieved Karthikeyan's car from the far side of the circuit, so will start the investigation into his problem before the end of this session.

Webber is going quicker on every lap. His best is currently a 1:38.952. It's still early days yet, so these times mean relatively little.

Hamilton sets the second fastest time immediately on his first lap of a five lap run on hard tyres. And is about to go even quicker...

Webber goes fastest in all three sectors again to clock a 1:38.483. Hamilton is currently 0.833 seconds off at the moment.

Reports from the pit lane suggest Heidfeld will not be back out on track as his mechanics have had to completely dismantle his brake.

Hulkenberg's Force India is currently the fastest through the speed trap at 303km/h. He would have been assisted by a combination of KERS (Kinetic Energy Recovery System) and the DRS (Drag Reduction System).

We apologise for the incomplete session data so far, we are working on rectifying the problem.

Webber is back on track. He's still the fastest man, 0.833 up on Hamilton and 1.960 up on Maldonado in third.

Liuzzi has now completed 9 laps but his best is 12.356 off Webber's pace.

Force India is keeping an eye on the sky: "Rain predicted...will it come in this session? Clouds look dull...."

Webber is back out on hard tyres and sets a time 0.225 off his best after a lock up in the final corner.

Alguersuari runs wide in turns 7 and 8 after a little mistake mid corner.

Button is lacking rear grip according to his radio transmission. Listening to his comments it sounds like they made some changes to the set-up but they've not worked. He's currently ninth fastest.

Liuzzi is now on a quicker lap, can he get close to the tail of the field?

Liuzzi clocks a 1:46.332. He is 7.849 off Webber and over two seconds off the slowest Lotus of Valsecchi.

Vettel goes 15th fastest after using his KERS on that last lap. Red Bull opted not to run KERS in Australia but are keen to get it working reliably this weekend.

Massa is on track at the moment but has not yet completed a flying lap.

Petrov is in the gravel at turn nine. His front-left brake exploded at about 170mph, pitching him into a spin. Possibly a similar problem to Heidfeld.

Petrov reckons the suspension broke but from the onboard footage it looked as if the wheel exploded, which would indicate a brake or hub issue. Hard to tell.

The official line from Renault is: "Vitaly's session is over. A technical problem in turn 9." A bit of an understatement, but it's too early to jump to any conclusions. We'll try to get to the bottom of that and report it on the website later today.

Karthikeyan is back on track in the HRT after that engine issue earlier.

Renault adds: "That's our morning session over. Nick will not have time to get back out."

Webber is on another quick lap... he goes 0.8 seconds faster than his earlier time with a 1:37.651.

Alonso runs wide at turn seven and into the gravel, but keeps the car running. Like several drivers this session, he lost the rear mid-corner and had to run wide to avoiud spinning.

Perez emulates Alonso and runs wide at turn seven too. Maybe the tyres are starting to go past their best after 15-20 laps of running.

Webber has completed plenty of laps with 21 to his name. Maldonado has done most with 30 and counting.

D'Ambrosio is off at the final corner with what looked like a suspension failure. The whole of the wheel and upright assembly came off under braking. He came to a safe stop in the gravel pit.

Yellow flags are out to allow the marshals to recover the Virgin in the gravel so no more fast laps are likely.

The session comes to an end with Webber comfortably fastest in the Red Bull, 1.665 up on Hamilton and 2.140 up on Schumacher in third.

His team-mate Vettel was 17th fastest, 3.976 off the fastest time. But don't read too much into these times as it's still very early in the weekend and we haven't seen any qualifying-style runs.

For a better idea of who's where ahead of the weekend make sure you join us for the second session in two and a half hours.