Ahead of today's opening session, the air temperature is 32 degrees C, while the track temperature is 52 degrees. It is bright and sunny, while humidity is 61%. Understandably, the FIA has designated this weekend a heat hazard event.

Before a wheel has turned, three drivers are facing grid penalties on Sunday. Colapinto, of course, following his reckless crash with Gasly and Norris and Lindblad and Hadjar, who have both taken on engine components which exceed their allowance.

In terms of upgrades, McLaren has a new Coke/Engine. To meet the high cooling demands of this and other upcoming circuits, this revised engine cover is aimed at increasing cooling massflow.

Red Bull has a new Floor Board. Applied above the existing floor foot geometry, this new board realises development work to extract more load locally whilst maintaining flow stability behind the front tyres.

Ferrari has a new Diffuser. However, this is not Sepang specific, however the very localized development around the diffuser winglet cascade provides a favourable additional downforce across the entire car operating envelope.

Racing Bulls have a new Front Wing and Rear Wing. A longer chord flap for the front wing that was introduced at Baku increases the load that can be generated by the wing, thereby meeting the aero balance requirements for this circuit, while an improved design of the rear wing support components allows the rear wing to perform more effectively, increasing the efficiency of load generated.

Haas has a new Rear Impact Structure. This additional rear impact structure device will enable targeted tuning of the car's characteristics for this circuit. Alpine has a new Front Corner. The front drum exit has been trimmed to increase brake cooling capacity, thereby improving thermal management for the upcoming high-demand tracks.

Other than a revised livery, in honour of partner Petronas, this weekend sees Mercedes introduce its much-anticipated - and much-feared, no doubt - upgrade. This includes a new Floor Board, Floor Leading Edge, Floor Corner, Floor Body, Rear Suspension, Rear Corner and Rear Bodywork. On the floor board, reprofiled elements and new vertical elements have been added to improve local pressure distribution, reduce separations at the extremes of the operating envelope, and improve flow to the rear of the car, resulting in increased load, while additional down-washing elements increase local load and outwash, improving flow to the rear of the car and increasing rear floor load. Re-optimisation of floor corner slot arrangement is to both increase local load and also improve flow into the diffuser and hence rear load, while through re-optimisation of the diffuser roof and sidewall the German team has increased local load and improved robustness throughout the operating envelope. In terms of the rear suspension, track rod and driveshaft camber has been re-distributed in order to increase local load whilst improving coupling with the diffuser winglet and rear drum furniture, while the chord and position of the rear drum winglets have been re-optimised to work with the fairing update and to improve rear tyre wake control across the operating envelope. Finally, the revised rear bodywork, with its reduced volume and increased sideview ramp, increases downwash to the rear floor and rear drum, resulting in more load.

Green light and Colapinto leads the way, followed by Hulkenberg, Ocon, Bortoleto and Bearman.

As more drivers emerge, it is mostly softs in use, though Colapinto, Lindblad, Hadjar and Verstappen are on softs.

Of the first wave, Antonelli (mediums), one of twelve drivers with no previous experience of the track, is quickest with a 40.137, until Verstappen responds with a 39.400.

Verstappen complains that his car is sliding a lot.

Russell goes second with a 39.627, as Colapinto, Hulkenberg and the Williams pair all pit without having posted a time.

Leclerc goes third, ahead of Antonelli and Hamilton.

In quick succession, both McLaren drivers run wide in Turn 14.

Verstappen improves to 38.883.

"This track is very cool," says newbie Russell as he improves to 38.932 and his teammate 39.454.

"Tyre deg is insane," reports Leclerc.

Understandably, with F1 not having been here since 2017, the drivers are keen to complete as many laps as possible.

"No brakes last corner," says Lawson, who subsequently gets the black and white flag for not keeping to the correct side of the bollard after running wide.

After 20 minutes, Hadjar is fourth, ahead of Leclerc, Hamilton, Lawson, Norris, Lindblad and Alonso.

A 39.197 puts Lindblad third, ahead of Antonelli.

In the Red Bull garage there is work going on at the rear of Verstappen's car.

It seems that Colapinto will also take a grid penalty for taking on more engine components.

As more drivers switch to softs, the teams having been caught out by the lack of grip, Hadjar goes top with a 38.303.

Lawson goes fourth with a 39.106, nut is demoted when a 38.590 puts Hamilton second.

Leclerc leapfrogs his teammate with a 38.367 as Russell, quickest in the two final sectors, stops the clock at 37.903.

Verstappen crosses the line at 37.520.

Antonelli improves but only to fifth, over a second off his teammate's pace.

Quickest in S1, Gasly goes seventh with a 38.715.

McLaren is running back-to-back tests with different rear wings - one of them the Macarena-style wing - on both cars.

Despite PBs in the final sectors, Alonso remains fourteenth, 2.1s off then pace, Stroll is currently 22nd, 4.1s down.

In the Red Bull garage, the TV camera picks up on blistering paint on the engine cover of one of the cars. Worrying.

With 15 minutes remaining, the Mercedes pair switch back to mediums.

In separate incidents, both Audi drivers are clearly struggling.

Hamilton, Gasly and Lawson follow Mercedes example and switch back to the yellow-banded rubber.

Russell runs wide in Turn 4, as does his teammate, while Turn 14 catches out Norris and Bearman.

Hadjar complains about traffic as Russell runs wide in Turn 14.

Having patiently followed Sainz through the opening complex after getting a tow from the Williams, Ocon deploys his energy perfectly to pass the Spaniard, only to run wide in Turn 4.

Asking about tyre deg on his car compared to rivals, Russell is told that the Mercedes is an "outlier".

The session ends. Verstappen is quickest, ahead of Russell, Hadjar, Leclerc, Antonelli, Hamilton, Gasly, Lawson, Lindblad and Hulkenberg.

Piastri is eleventh, ahead of Norris, Bortoleto, Alonso, Ocon, Bearman, Albon, Stroll, Colapinto, Sainz, Bottas and Perez.