Mercedes' Lewis Hamilton of Britain drives during the second practice session of the Japanese Grand Prix at the Suzuka circuit on Friday. Photo: IC

Red Bull's Russian Daniil Kvyat led a rain-swept Japanese Grand Prix practice on Friday as bad weather kept Formula One guessing about who would come out on top at the weekend.

Mercedes' championship leader Lewis Hamilton was fifth and third fastest in the two sessions, while teammate and title rival Nico Rosberg was third and second, but times were meaningless.

Hamilton spent much of his day sheltering from the rain, completing only six laps in the morning and eight in the afternoon.

"There was not much to learn," the Briton, whose team's dominance mysteriously disappeared in Singapore on September 20, told the BBC. "It is irrelevant what we did today, with the weekend going to be dry."

Mercedes motorsport head Toto Wolff added, "If you don't need to test any new items on the car, there is no need to take a risk in these ­conditions."

Eight of the 20 drivers failed to set a time in the morning session, with cars throwing up plumes of spray when they did go out on a slippery track.

Spanish rookie Carlos Sainz was fastest before lunch for Toro Rosso, despite problems with aquaplaning on a track with improved drainage after the late Jules Bianchi's tragic accident last year.

Sainz's best time of 1 minute 49.434 seconds compared to Kvyat's 1:48.277 in the afternoon.

It was the first time in his 14-race career that Sainz had led a session, while Renault had the rare accolade of seeing their engines top the times in both.

Kvyat had been second in the morning.

Ferrari's Sebastian Vettel, winner from pole position in Singapore for his third victory of the season, was fourth and fifth quickest in the respective sessions.

Vettel's speed in Singapore raised questions about whether Mercedes were suffering circuit-specific problems or whether Ferrari and Red Bull had managed to rein in their hitherto dominant rival.

Suzuka, a fast track with challenging corners, should be much more to Mercedes' liking but both Hamilton and Rosberg had hoped for more reassurance than they were able to get from Friday's sessions.

Financially-struggling Lotus, whose freight was delivered only on Thursday, remained locked out of their paddock hospitality - where teams and guests are catered for - due to payment problems.

Lotus reserve driver Jolyon Palmer, replacing Romain Grosjean for the session, managed only an installation lap.

The Briton later tweeted a picture of himself "enjoying" the team's VIP hospitality - sitting on the floor of the garage with a packet of crisps.