Lewis Hamilton says he expects a "serious fight" with Ferrari at the British Grand Prix this weekend.
Mercedes were expected to lead the way at Silverstone but Ferrari's Sebastian Vettel was quickest in second practice.
Hamilton said: "It's going to be very, very close this weekend. The Ferraris are really fast. We're in for a serious fight, which is great for the fans. I hope we pull through."
Vettel said: "They are very strong around here. I hope we can be there."
The German was 0.187 seconds clear of Hamilton in second practice on Friday.
Hamilton set the overall fastest time of the day in first practice, 0.065secs faster than Vettel's fastest lap in the second session and 0.5secs ahead of the Ferrari in the same conditions in the morning.
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Victory on Sunday would be a record sixth British GP victory for Hamilton, and would take him ahead of Sebastian Vettel in the drivers' championship, in which the German currently leads by one point.
Hamilton said he was loving the experience of driving at the fast, sweeping Silverstone circuit, in front of tens of thousands of adoring fans. He was revelling in the Mercedes' ability to take the 190mph first corner, Abbey, flat out while also using the DRS overtaking aid, which reduces aerodynamic downforce and grip.
Hamilton said: "The atmosphere has been great - the weather is fantastic and the crowd was incredible.
"The track is the fastest it has ever been; we're flat out through Copse, and Turn One and through Turn Two with the DRS - it's insane how fast it is. The faster this track gets, the better it gets. It has to be the best track in the world, it feels like driving a fighter jet around the track.
"However, it is also the bumpiest track I've ever experienced. With the speeds we're going now and the G forces we're pulling, I think it's going to be the most physical race of the year."
Vettel added: "I expect them to be very strong tomorrow (in qualifying), but I hope it is going to be close. That would be very good news. Historically it has not been a very strong track for us."
Vettel wishing England well at the World Cup
Vettel said he was hoping England would progress beyond their World Cup quarter-final match with Sweden, which starts as qualifying finishes at 15:00 BST on Saturday.
The 30-year-old - who is something of an anglophile, and a fan of Fawlty Towers and The Beatles - said: "I hope England goes far - and I mean it, because obviously the last World Cups many of them haven't been good for you guys.
"I don't think you have anything to fear if it goes to penalties either."
Hamilton says he wants to watch the match, and has joked with the media delegate for governing body the FIA about missing the mandatory post-qualifying news conference.
Hamilton said during an earlier news conference at Silverstone: "We always come to the grand prix with some epic sport surrounding it, be it Wimbledon or whatever.
"I was actually going to ask what is the penalty for missing the press conference on Saturday. Is it negotiable? I want to be watching the game."
Hamilton also revealed that he is planning to travel to Russia to see the World Cup final next weekend.