The Latest on motorsport's busiest day (all times local):
3:50 p.m.
With six laps to go, defending Formula One champion Lewis Hamilton was leading the Monaco Grand Prix ahead of Red Bull's Daniel Ricciardo and on course for his first win of the season.
Hamilton has not won for the past eight races, but was 2 seconds ahead. Ricciardo was running out of time to overtake Hamilton's Mercedes on the tight and twisty track.
Mexican driver Sergio Perez was well poised for a podium as the Force India driver was in third place ahead of Sebastian Vettel's Ferrari.
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3:30 p.m.
The wrecks continue at the Monaco Grand Prix, this time with Sauber teammates Felipe Nasr and Marcus Ericsson getting into each other.
Nasr received team orders to let Ericsson through but apparently ignored them. A determined Ericsson went for a gap that simply did not exist and they both collided at the Rascasse turn.
Ericcson quipped that his teammate's radio ''musn't be working.''
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3:15 p.m.
Mercedes driver Lewis Hamilton is leading a thrilling Monaco Grand Prix, with Red Bull driver Daniel Ricciardo pressuring him as he tries to overcome a huge error from his own team.
With 45 of 78 laps completed, Hamilton was 0.4 seconds ahead of Ricciardo, who went close to overtaking Hamilton on lap 37. But Hamilton held his line at the Mirabeau turn, prompting an angry reaction from Ricciardo, who waved his hand furiously as he was forced to back off.
After the track dried out following teeming rain all morning, Hamilton came in for quicker ultra-soft tires on lap 32, with Ricciardo coming in a lap later to switch to the same tires.
In an astonishing oversight by Red Bull, Ricciardo's pit crew was not ready and this cost him valuable time as he came out behind Hamilton.
Nico Rosberg, the points leader for Mercedes who has won seven of the last eight F1 races and the last three at Monaco, had slipped to sixth place.
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3:05 p.m.
Red Bull's Max Verstappen - who became the youngest winner of an F1 race at the Spanish GP two weeks ago - has crashed out of the Formula One race in Monaco.
On a day with slippery conditions on the track, the 18-year-old slammed into a barrier at the same point where he crashed in Saturday's third and final practice.
He is the fourth driver to crash out on a chaotic day: Russian driver Daniil Kvyat got into the turn at La Rascasse, taking Kevin Magnussen into the barriers with him.
Kvyat, who has twice been blamed for racing incidents with Ferrari driver Sebastian Vettel this season, went out of the race, while Magnussen carried on a lap behind.
Ferrari driver Kimi Raikkonen and British driver Jolyon Palmer - Magnussen's teammate at Renault - both crashed earlier.
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2:30 p.m.
After seven laps behind a safety car, British driver Jolyon Palmer crashed out and was soon joined back in the garage by Ferrari driver Kimi Raikkonen.
Raikkonen lost control of his car after breaking too late going into a hairpin, locked his wheels and slammed into the barrier.
He tried to continue but almost caused another collision, with French driver having to brake sharply to avoid smashing into the back of him.
''What's Kimi doing?'' screeched Grosjean.
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2:20 p.m.
The Monaco Grand Prix has got off to a difficult start - and they haven't even started racing yet.
On a soaking wet track, with spray streaming off the tires, drivers did seven laps behind a safety car as a precautionary measure.
This was not to defending F1 champion Lewis Hamilton's liking, who after four laps said over team radio that ''visibility is as good as it's going to get. We should just start the race.''
Then, just as drivers had been called in to get ready to start the race, the race was held up again when British driver Jolyon Palmer's car skidded and crashed into the barriers, with both his front wheels on his Renault mangled.
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1:45 p.m.
Formula One champion Lewis Hamilton is in pensive mood at the Monaco Grand Prix - and with good reason.
The three-time world champion has not won any of the past eight races, while his Mercedes teammate Nico Rosberg has won seven of them to take a commanding lead in this year's F1 title race.
As he waited for the driver's pre-race parade to start, Hamilton looked in contemplative mood as he leant against a railing with his headphones on and a hot drink in his hand.
Rain fell heavily all morning and briefly abated before returning just before the start of the race, with drivers huddling under umbrellas.
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1:25 p.m.
The Monaco Grand Prix traditionally sees an influx of movie stars from nearby Cannes, where the famous film festival is held.
This year, the events are a week apart and there's a notable absence of big names so far.
However, actor Patrick Dempsey - a long-time star of ''Grey's Anatomy'' and a huge motorsport fan - is in the paddock.
The 50-year-old American has been chatting with Red Bull driver Max Verstappen and Frenchman Romain Grosjean - who drives for the American-based Haas team - before the race.
There is more of a sporting flavor than a Hollywood theme, with basketball stars Chris Bosh (Miami Heat) and Tony Parker (San Antonio Spurs) and International Olympic Committee president Thomas Bach all present.
Bosh, pictured on his twitter feed wearing a Mercedes cap, has expressed his support for Lewis Hamilton.
Arsenal soccer star Theo Walcott and Danish tennis player Caroline Wozniacki are also here.
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1 p.m.
The Monaco Grand Prix is all glitz, glamour, blue skies and luxury yachts swaying on the glittering blue Mediterranean sea, right?
That's often the case, but it has been raining all morning in the Principality and fans have been huddling under umbrellas.
With one hour to go before the race, the rain has at least stopped - which might not be good news for Formula One champion Lewis Hamilton.
After finishing third in Saturday's qualifying, Hamilton wrote off his chances of winning - because it's so hard to overtake on the tight and sinewy street circuit - and joked that he would need a downpour to make the race more unpredictable.
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