Ahead of today's opening session, the air temperature is 17 degrees C, while the track temperature is 20 degrees. While, according to Race Control, there is 0% chance of rain in this session, we are expecting some wet stuff over the next two days.

There are no reserve drivers on duty this morning, while a couple of teams are running the halo in anticipation of its introduction next year.

Alonso is among the first out but the Spaniard immediately encounters an issue. He tells his team that it is unlikely that he will make it back to the pits... but he does.

Five minutes into the session everyone has been out but there are no times on the door.

After a brief lull, Ocon heads out, followed by Massa and Stroll. The Frenchman, on the supersofts, posts the first time of the weekend, crossing the line at 1:48.962.

Early problems for Massa who goes off into the barriers at Malmedy. The driver is OK, which is more than can be said of the car. "I lost the car on the kerb," he reports.

The session is red-flagged.

The Brazilian, who was given the all-clear by the FIA following the illness that kept him out of the Hungarian Grand Prix, heads back to the pits, as does his FW40 which has incurred significant damage to its right-side.

The session resumes... and Ocon is warned not to pass the red light, the Frenchman leading a whole gaggle of eager beavers keen to get back to work. In moments there are 16 drivers on track.

Sainz posts the second time of the day (49.769) with Perez posting 48.766 moments later.

A number of drivers, including Hamilton, miss the apex at Raidillon, as Magnussen complains that his headrest is loose... a claim borne out by the TV cameras.

That mad rush to get out naturally leads to a flurry of times and as the smoke clears Hamilton is quickest (47.410), ahead of Ricciardo, Verstappen, Raikkonen and Vettel.

That said, Vettel was on softs, the Red Bulls on ultras and Hamilton and Raikkonen on supers.

Bottas is told that Hamilton is reporting that his tyres are overheating quickly.

Ricciardo posts 46.838 to go quickest as Raikkonen improves to 46.931.

After 36 minutes, Vandoorne, Wehrlein and Massa have yet to post a time, the latter two unlikely to anytime soon following the Brazilian's crash and the fact that the Sauber is up on its stand.

As if to emphasise his tyre issues, Hamilton slips and slides at La Source. The Briton subsequently calls on his team to find him a gap in the traffic.

Hamilton retakes the top spot with a 46.439 as Bottas posts 47.074 to go 4th. The Finn subsequently improves to third with a 46.903.

Vandoorne finally posts a time, the Belgian stopping the clock at 49.140 to go 12th, his teammate currently 15th.

Hulkenberg pits are complaining that his seat is getting a bit warm.

Later than usual, there is a lull as the teams hand back their extra set of tyres.

With 35 minutes remaining, after several minutes of silence, Ocon once again gets proceedings underway. Meanwhile, in the Ferrari garage, mechanics are working on the front brakes on Raikkonen's car.

Hamilton is currently quickest, ahead of Ricciardo, Bottas, Raikkonen, Verstappen, Vettel, Ocon, Sainz, Perez and Vandoorne. The top four are covered by 0.492s, Hamilton and Raikkonen on supers, Ricciardo on ultras and Bottas on softs.

As Hamilton follows his teammate's example and switches to the yellow-banded rubber, Bottas posts 46.424 to go top. The Finn subsequently runs wide and through the gravel at Fagnes, doing well to merely brush the barriers and not do too much damage.

Ricciardo is the latest in a string of drivers to miss the apex at Raidillon.

A 45.555 sees Hamilton go quickest, while Alonso reports that his DRS is not working. Nonetheless, the team asks him to continue.

Grosjean - surprise, surprise - complains of a problem with the front-left "under braking".

Still on the ultras, Verstappen improves to second with a 46.302 then promptly gets it wrong at the final chicane, thereby bringing out the yellows.

Kvyat complains of "strange engine behaviour".

Now on the ultrasoft, Vettel, currently 9th (47.856), improves to second with a 45.647, just 0.092s off Hamilton's pace. He wasn't quickest in any of the sectors, just PBs all round.

A big wobble for Stroll in Les Combes but he keeps it all together.

"There's a vibration in these tyres," warns Hamilton.

Bottas in back on track following his earlier 'moment'.

A late charge sees Raikkonen go quickest on the ultras, the Finn crossing the line at 45.502, leaving Hamilton - who's best was on softs remember - 0.53s in his wake.

Raikkonen is told that Vettel lost a lot of his front tyre temperature on his "charge lap" and is advised to keep his temperatures up.

The session ends with Raikkonen quickest, ahead of Hamilton, Vettel, Verstappen, Ricciardo, Bottas, Sainz, Ocon, Kvyat and Vandoorne.

Palmer is eleventh, ahead of Hulkenberg, Alonso, Perez, Stroll, Magnussen, Grosjean, Ericsson, Wehrlein and Massa.

Strong pace from the Ferraris, but pretty incredibly pace from the Mercedes duo, especially Hamilton, considering they were on softs as opposed to ultras.

Check out our Friday gallery from Spa, here.