|Singapore Grand Prix on the BBC|
|Venue: Marina Bay Circuit Date: 18-20 September|
|Coverage: Highlights on BBC TV, coverage on BBC Radio 5 live and sports extra, online, mobile, the BBC Sport app and Connected TV|
Lewis Hamilton says Mercedes face a "genuine" threat from Red Bull and Ferrari at the Singapore Grand Prix.
The world champion was fourth fastest in second practice at Marina Bay.
Red Bull's Daniil Kvyat was quickest, with team-mate Daniel Ricciardo third and Ferrari's Kimi Raikkonen second.
Briton Hamilton, who leads the drivers' standings by 53 points, said: "There are no problems with the car but everyone looks closer, if not a bit faster."
He ended the second session 0.337 seconds behind Kvyat, while the second Ferrari of Sebastian Vettel was fifth fastest, 0.008 secs slower than Hamilton.
Hamilton added: "The car feels good but the others are much closer this weekend. It's always the case here.
"We'll still be fighting. We just need to work hard and find out where the time is."
Ricciardo said he believed Mercedes had plenty in hand.
"I hope this is their real pace," said the Australian. "But I am sure they will turn it up and find a way. I am sure Mercedes will fool everyone.
"We will aim for [pole]. Whether we will get it or not is another thing. We will do what we can to get as far up the grid as we can possibly get."
Four-time world champion Vettel said: "It was a good day for us. The car seems to work and we can still improve.
"Obviously the Mercedes will be quick. I don't know what happened to them today; they looked a bit slow.
"But I'm sure they will change it for Saturday. We know some of the Mercedes team usually don't show everything on Friday."
Singapore GP is a modern classic
Singapore has been on the Formula 1 calendar only since 2008, but already it has become a modern classic.
The key was to hold the street race in the south-east Asian city state at night.
The combination of futuristic skyscrapers across the cityscape, colonial buildings lining the circuit and the lighting on the paintwork of the cars is stunning.
The tight and twisty track does not always produce the greatest race, but as a challenge it is among the toughest in the sport - the combination of tropical heat and humidity, the bumpy track and the longest event on the calendar tests the drivers to their limit.