Ahead of today's opening session the air temperature is 17.6 degrees C, while the track temperature is 21.1 degrees. It is cloudy and damp and though it is not currently raining the session is declared wet.

In terms of updates, Mercedes has a new front wing endplate, floor fence and edge, together with new rear wing flap and tips, while Red Bull has a new engine cover and rear wishbone shroud and Ferrari a new rear wing and beam wing.

McLaren has a new diffuser, rear wing, beam wing, rear brake winglet, engine cover, cooling louvres and front track-rod fairing, while Alpine has new rear brake ducts and floor fences and Alpha Tauri a new rear wishbone shroud, rear brake winglets, rear wing and beam wing.

At Aston Martin there are new front wing flaps and a new rear wing, while Williams has new front wing flaps, rear wing flaps and beam wing.

Alfa Romeo has new front wing flaps, rear wing flaps and endplates, and Haas new rear brake winglets and beam wing.

There is one reserve driver on duty his morning, Liam Lawson taking over Pierre Gasly's AlphaTauri.

The lights go green and Sainz leads the way, followed by Russell, Albon, Lawson, Verstappen and Perez.

As more drivers head out, all are sporting Inters, however Sainz pits for hards while Alonso and Norris opt for softs. Ricciardo goes medium.

Sainz posts the first time of the weekend, a 1:51.622.

Norris raises the bar with a 49.712, as Ricciardo goes second (50.958), ahead of Sainz, Leclerc and Alonso.

Verstappen claims Latifi was unsafely released, though video replay suggests six of one and half a dozen of the other.

Ocon goes second (50.315), ahead of Leclerc and Sainz, but Ricciardo responds with a 50.010.

"I have a problem, guys," reports Ocon, who feels it is a diff issue. He is told to bring the car back slowly.

A 47.456 sees Verstappen (softs) go quickest, ahead of Perez, Ricciardo and Norris. The world champion subsequently improves to 46.755.

A number of drivers are expected to take on new power units tomorrow, including title challengers Verstappen and Leclerc, which would be welcome news for Mercedes.

On the mediums, Hamilton improves to sixth with a 49.408.

In the Alpine garage Ocon climbs from his car, his issue appearing to be terminal.

Hamilton improves to second with a 48.420, 1.665 off Verstappen's pace.

From out of nowhere, Albon (softs) goes second with a 48.112, still over a second off Verstappen's pace.

On board footage of Albon's Williams reveals that, despite the technical directive which comes in this weekend, bouncing remains an issue.

On softs, Sainz goes quickest with a 46.538, as Magnussen grinds to a halt just after La Source. "Engine is out," reports the Dane.

The session is red flagged. The car is live so it is some time before mechanics are able to approach it.

As the session remains under the red flag, race control confirms new power unit components for a number of drivers including Verstappen, Norris, Ocon, Bottas and Leclerc, resulting in a number of penalties for Sunday.

The session resumes with 9 minutes remaining. Alonso leads the way, followed by Verstappen, Vettel, Stroll and Zhou.

"There is a risk of a shower," Verstappen is warned. Ricciardo is given a similar warning, advised that Turns 14 and 15 (Campus and Stavelot) will be hit first.

At Alfa, Bottas has only completed two laps and has yet to post a time.

The rain begins to fall and as a result the drivers, who are all on slicks, ease off and head back to the pits.

The McLaren pair switch to Inters and head out again.

Leclerc is asked if he thinks it is safe to continue on his mediums. "For now I drive," he replies, and promptly runs wide.

As more drivers switch to the Inters, the rain intensifies.

The session ends. Sainz is quickest, ahead of Leclerc, Verstappen, Russell, Stroll, Albon, Ricciardo, Tsunoda, Hamilton and Perez.

Latifi is eleventh, ahead of Zhou, Norris, Alonso, Vettel, Ocon, Magnussen, Schumacher, Lawson and Bottas.

Check out our Friday gallery from Spa here.