World champion Valentino Rossi laid down an early marker with the quickest time in practice for the China Grand Prix at a wet Shanghai international circuit on Friday.

Rossi has four riders above him in the championship standings. [AFP]

Despite questions about his ability in wet conditions, the 27-year-old Yamaha rider topped the times in both of the day's sessions.

His best lap of 2:09.393 came on his last run around the 5.3-km circuit.

Loris Capirossi, who won the opening race of the season for Ducati and is second in the title race, set the second best time of the day on his final lap, just 0.355 seconds slower than fellow Italian Rossi.

The seven-times world champion, who won the inaugural MotoGP race in China in torrential rain last year, is in the unusual position of having four riders above him in the standings going into the fourth round of the championship.

American John Hopkins's time of 2:10.007 for third fastest showed Suzuki have the pace to challenge this season, although his Australian team mate Chris Vermeulen, who took pole at the last race in Turkey, had to be satisfied with 11th fastest on Friday.

Spain's Sete Gibernau's challenge to Rossi's supremacy two years ago was largely built on his proficiency in the wet and he was fourth quickest for Ducati ahead of championship leader Nicky Hayden.

Hayden was the best Honda rider on the day although Italian Marco Melandri, the winner in Turkey, and impressive rookies Dani Pedrosa of Spain and Australian Casey Stoner were bunched behind him for the Japanese manufacturer.