Carlos Sainz tops washed-out opening free practice session for Belgian Grand Prix

Ferrari driver Carlos Sainz topped a rain-hit practice session for the Belgian Grand Prix.

With persistent rain falling at Spa-Francorchamps, not one driver completed more than eight laps.

Sainz headed the timing charts, half-a-second clear of McLaren's Oscar Piastri with team-mate Lando Norris third.

Max Verstappen, who is set to serve a five-place grid penalty following a gearbox change, was among five of the 20-strong field who did not complete a timed lap.

Qualifying is due to take place at 5pm local time (4pm BST), but the running is under threat given the bad weather and poor visibility generated by the spray in the Ardennes.

Formula One's governing body, the FIA, said their priority is to ensure qualifying for Sunday's main event takes place with other sessions throughout the weekend - including Saturday's sprint schedule - likely to be sacrificed.

Heavy rain is expected to continue on Friday, and into Saturday with conditions forecast to improve on Sunday. One option is to move qualifying to Sunday morning, as the FIA did in Japan in 2019 when Typhoon Hagibis struck.

If qualifying can not take place, the FIA confirmed the grid for Sunday's main event will be set by championship order.

Conditions worsened through Friday's one-hour session with Logan Sargeant crashing out at the midway stage.

The Williams rookie lost control of his car under braking for Les Combes, heading straight into the barrier. The American was unharmed in the accident but the red flags were deployed to recover his stricken machine.

Alfa Romeo's Zhou Guanyu also grazed the barrier after he ran through the gravel.

The FIA's decision whether or not to run in the wet conditions will be heightened following the death of 18-year-old Dilano Van 't Hoff at Spa-Francorchamps earlier this month.

The Dutch teenager was killed after a crash in a rain-hit Formula Regional European Championship (FRECA) race on July 1.

1 Carlos SAINZ Ferrari 2:03.207

2 Oscar PIASTRI McLaren +0.585

3 Lando NORRIS McLaren +1.277

4 Charles LECLERC Ferrari +4.941

5 Sergio PEREZ Red Bull +5.033

6 Alexander ALBON Williams +5.187

7 Yuki TSUNODA AlphaTauri +5.860

8 Kevin MAGNUSSEN Haas F1 Team +6.022

9 Daniel RICCIARDO AlphaTauri +6.112

10 Nico HULKENBERG Haas F1 Team +6.835

11 Fernando ALONSO Aston Martin +7.076

12 Lewis HAMILTON Mercedes +7.092

13 George RUSSELL Mercedes +7.268

14 Valtteri BOTTAS Alfa Romeo +8.878

15 Guanyu ZHOU Alfa Romeo +10.795

16 Logan SARGEANT Williams no time

17 Lance STROLL Aston Martin no time

18 Pierre GASLY Alpine no time

19 Esteban OCON Alpine no time

20 Max VERSTAPPEN Red Bull no time