Ahead of today's opening practice session, the air temperature is 30.1 degrees C, while the track temperature is 54.8 degrees. It is bright, sunny and hot.

In terms of updates, Mercedes has a new floor edge and front brake ducts, Red Bull new floor fences and rear brake winglets, Ferrari new floor (front/mid & diffuser) and McLaren a new rear wing endplate, sidepods, engine cover, cooling louvres, floor & diffuser and rear brake ducts.

Alpine has a new floor (strakes & fences), also Alpha Tauri (fences, edge, diffuser), and a new engine cover, while Aston Martin has a new floor edge, Williams a new floor (forward mounting) and Alfa Romeo a new rear brake deflector.

In the moments before the start of the session the race director makes a change in terms of track limits whereby his stipulation that: "In accordance with the provisions of Article 33.3, the white lines define the track edges. During Qualifying and the Race, each time a driver fails to negotiate with the exit of Turn 10, will result in that lap time and the immediately following lap time being invalidated by the Stewards", actually becomes... "In accordance with the provisions of Article 33.3, the white lines define the track edges."

There are two reserve drivers on duty this morning, Nyck de Vries takes over Lewis Hamilton's Mercedes, whilst Robert Kubica is in Valtteri Bottas' Alfa Romeo.

The lights go green and Sainz is first out, followed by Kubica, Zhou, Albon and Gasly. As more drivers head out, among them is de Vries, who previously took part in FP1 in Spain with Williams.

The cameras pick up on two legends in the Ferrari garage, Messrs Alain Prost and Jean Alesi.

As Sainz posts the first time of the weekend, a 39.577, he is sporting the softs, though most are on the mediums. That said, Vettel is on hards.

Magnussen posts a 38.157, Norris a 37.604, Leclerc a 37.420 and Verstappen a 35.727, the Dutchman quick straight out of the box.

De Vries first lap is good enough for seventh (39.583), while a 37.420 sees Leclerc close to within 1.693s of his main title rival.

"I can't go like this anymore, engine problem," reports Gasly." "Yes, we see the issue," the Frenchman is told. He subsequently pits.

A 36.162 sees Perez go second, as teammate Verstappen improves to 34.991.

Behind the Bulls, Ricciardo is third (36.766) and Norris fourth, but both are demoted when Leclerc posts a 35.821 to split Verstappen and his teammate.

Perez reclaims second with a 35.562, but remains 0.571s off his teammate's pace.

Alonso goes fifth with a 36.972, but is demoted when de Vries stops the clock with a 36.322.

Back on track following his earlier issue, Gasly goes seventh with a 37.078.

Perez spins at Turn 3, the back end of the Red Bull suddenly snapping out. He picks up a massive flat spot in the process.

Russell goes fourth with a 35.851, ahead of Gasly, de Vries, Ricciardo and Alonso.

Sainz, who is currently 18th, will incur a grid penalty as he has taken on new control electronics and thereby exceeded his allowance. It is widely expected that the Spaniard will take on a whole new power unit this weekend to add to his pool.

At which point the Ferrari driver improves to fifth with a 36.042.

"Something's really odd, because I've kept it at full throttle but the car's not accelerating," reports Kubica.

Ricciardo runs wide at Turn 12, his tyres seemingly shrieking in pain as they encounter the circuit's unique run-off strips.

While the majority are on softs or mediums, Albon and Vettel are on hards.

On a fresh set of softs, Verstappen improves to 34.346, however Sainz responds with a blistering 34.268 to go top by just 0.078s.

As Russell switches from mediums to softs, de Vries (softs) goes third with a 35.426.

Perez pits to have a rogue tear-off removed from his rear suspension.

Verstappen complains that "out of 9" his upshift was "massively delayed". "That shouldn't happen," he warns.

Verstappen goes quickest in the opening two sectors, and despite a mistake in Turn 10 still goes top with a 34.021. "I understeered a bit wide," admits the Dutchman.

From out of nowhere, Albon produces a 35.414 to go sixth, this being the first weekend where teammate Latifi has the upgrade first introduced at Silverstone.

A 34.104 sees Leclerc get to within 0.083s of Verstappen's pace. The Monegasque subsequently posts a 33.930, thereby eclipsing Verstappen by 0.091s.

Gasly improves to fifth with a 34.979, while countryman Ocon is currently 19th.

Gasly subsequently asks for the car to be checked after "bottoming out".

"Do I have time to go to the toilet," asks Norris. Told "no", he replies: "Well I do need to!" The McLaren driver is currently 7th.

In quick succession, Gasly and Vettel run wide at Turn 11.

With a couple of minutes remaining, all twenty drivers are on track.

In the Red Bull garage Adrian Newey oversees work on Verstappen's car following his off.

Thus far, Tsunoda leads the way in terms of the number of laps completed (26), ahead of Russell (25), Vettel and Albon (24) and Leclerc, de Vries and Latifi (23).

The session ends. Leclerc is quickest, ahead of Verstappen, Sainz, Russell, Gasly, Perez, Norris, Albon, De Vries and Ricciardo.

Zhou is eleventh, ahead of Stroll, Ocon, Vettel, Alonso, Schumacher, Magnussen, Tsunoda, Kubica and Latifi.

Check out our Friday gallery from Le Castellet here.