Just under 20 minutes left on the clock, folks.

And it's as you were at the top of the standings.

Charles Leclerc's 1:23.008 leads the way, followed by George Russell three tenths behind and then Lewis Hamilton.

Not a bad showing from Ferrari in this first session.

I'm not sure what's gone on there but Kimi Antonelli goes into the gravel at the turn one chicane...and he's followed by Lando Norris...and then Carlos Sainz.

They all make the same last-ditch move off-track. How strange.

Image source, Getty Images

The two Ferraris sandwich second-placed George Russell right now as Lewis Hamilton goes third fastest.

Championship leader Kimi Antonelli, with a new engine for this weekend, is fourth.

Charles Leclerc gives the Tifosi reasons to be cheerful as he guides his Ferrari into top spot with a 1:23.008.

Further down the order, Paul Aron's currently the best of the rookies as he occupies 13th place so far.

Andrew Benson
BBC F1 correspondent at Monza

McLaren have won their appeal against the result of the Monaco Grand Prix after a controversy over multiple incorrect pit-lane speeding penalties.

The victory means Alpine's Pierre Gasly loses the podium he was awarded after an appeal by the French team that overturned two five-second penalties.

That means Gasly, who finished third on the road, is dropped back to the seventh place he received in the official results.

Red Bull's Isack Hadjar is returned to third place and McLaren's Oscar Piastri fourth for the race which took place on 7 June.

There were multiple speeding penalties because Formula 1 had incorrectly measured the length of the pit lane, meaning cars' average speeds were adjudged wrongly to be too high.

Read more on the developing story here.

Image source, Getty Images

And the pit lane is back open. We've lost the best part of five minutes of the session, there.

Given how infrequent these rookie FP1 sessions are, that's bad luck for Colton Herta if his time behind the wheel of Sergio Perez's Cadillac is over.

The session will resume at 12:56 local time.

That's 11:56 BST.

So while we wait for things to get going again. What's the lay of the land?

Well Lando Norris, fresh from two successive Grand Prix victories, leads the way with a 1:23.719 in his McLaren.

Just 0.083 seconds separates him from George Russell while Lewis Hamilton makes it an all-British 1.23 top three with his 1:23.891.

Red flagpublished at 11:50 BST

11:50 BST

The marshals are trying their best to give Colton Herta's Cadillac a nudge with the car seemingly stuck in gear.

In the mean time, the session is red flagged with the car still stuck at the side of the track.

Colton Herta's come to a standstill just beyond turn five.

The rookie pulls his Cadillac to the side of the track. Not great just 20 minutes into the session.

There's not a set tyre choice right now on track. It's a mix between hard and medium so far.

But Kimi Antonelli has joined Liam Lawson in donning a set of softs.

The times are getting faster by the minute.

Lando Norris initially sets a 1:24.194 on the medium tyre but George Russell betters him by almost four tenths with a 1:23.802.

We're into the 1:23s now. The conditions are perfect, unlike at Zandvoort this time two weeks ago.

Lewis Hamilton is the fastest man on track now.

He hauls his Ferrari into a 1:24.291 and with a set of hards on, no less.

The Tifosi love that.

Image source, Getty Images

The times are tumbling down as you might expect at this point in the session.

Liam Lawson, who thus far is the only car to set a lap on the soft tyre, sets a 1:24.383 and goes top of the tree.

A reminder that he's back in the Red Bull with Isack Hadjar still out with a wrist injury.

No sooner does Charles Leclerc go fastest does George Russell move into top spot.

His 1:25.259 is the pick of the bunch so far.

Huge cheers as the Ferrari of Charles Leclerc goes out on track.

He puts down a 1:26.873 and goes fastest in the early stages of this session.

Rebecca Clancy
F1 journalist on BBC Radio 5 Sports Extra

I don't think this track will quite favour the McLaren but it could be a four-way fight for the victory. I think it's going to be a very, very tight weekend.

We've got four rookies taking part in FP1 today.

Ayumu Iwasa has stepped into Max Verstappen's Red Bull, Luke Browning has replaced Alex Albon at Williams and Paul Aron is in for Pierre Gasly at Alpine.

Meanwhile, Colton Herta - who it feels weird to call a rookie given he's been such a stalwart in IndyCar - is in for Sergio Perez at Cadillac.

Right then, let's get going.

We've gone green and we are under way at Monza.

Rebecca Clancy
F1 journalist on BBC Radio 5 Sports Extra

I adore Monza. I'm here for the romance. The tifosi are incredible, the history here, the atmosphere. It's gearing itself up for a fantastic weekend.