|Perez's wrecked Sauber is hoisted away after the third crash at the Monte Carlo street circuit [GALLO/GETTY]
World championship leader Sebastian Vettel secured his fifth pole position of the season after posting the fastest time in Saturday's crash-marred qualifying session at the Monaco Grand Prix.
Vettel's best lap time of 1 minute, 13.556 seconds gave Red Bull its sixth straight pole, ahead of McLaren's Jenson Button and Vettel's teammate Mark Webber.
"If you'd asked me before qualifying if I would have taken third, I probably would have," Webber said.
Webber took pole at last week's Spanish Grand Prix, Vettel took the previous four poles and already leads McLaren's Lewis Hamilton overall by 41 points as he bids to win in Monaco for the first time.
It was a disappointing session for Ferrari's Fernando Alonso, who was quickest in the final practice on Saturday morning, but dropped to fourth in qualifying.
Mexican driver Sergio Perez became the third driver to crash at the Monaco Grand Prix this year, racing out of the tunnel and skidding across the track late in the afternoon's qualifying session.
The Sauber driver lost control of his car as he was about to come out of the tunnel, and the front slid over to the right and slammed into the tunnel barrier. The car then span round and hit a tire wall on the circuit.
"It's difficult to keep the focus and it's difficult to keep the concentration when you don't know what's going on," Vettel said.
A medical crew rushed to Perez's car, and a giant blanket was immediately draped over it. After a few minutes the battered car was lifted off the track.
Sauber team official Hanspeter Brack told reporters: "Sergio was conscious and he has been talking. He is now being brought to the hospital and we will have to wait for further information."
Mercedes driver Nico Rosberg and Hispania's Vitantonio Liuzzi were both unharmed after crashing in practice earlier on Saturday.
Rosberg crashed at almost exactly the same spot as Perez, who is racing in his debut season, but the Mexican's accident was more violent.
One of the Sauber car's tires rolled down the track seconds after the car had slammed into the tire wall, and another incident was thankfully avoided as there was no other car immediately behind Perez.
Jenson Button had a similar accident at the same spot in final practice with BAR Honda in 2003.
"I know how much it hurts (to crash there)," said Button.
"I'm not sure he'll be racing tomorrow but hopefully he'll be watching."
Perez's crash severely hampered Hamilton, as he had yet to set a lapped time and the heat went out of his tires as he waited nearly 40 minutes for qualifying to resume.
The 2008 F1 champion will start Sunday's race down in seventh spot, a disappointment for the English driver, who was fastest in both the opening two qualifying sessions.
Early into Saturday's morning practice, Rosberg walked away unharmed when the German driver ploughed into a crash barrier after flying out of the tunnel and swerving off to the right.
Toward the end, a second red flag went up when Liuzzi crashed sideways into the barriers at the Sainte Devolte turn.
The Italian was also unharmed and his Hispania car was airlifted away.