Nico Rosberg headed Lewis Hamilton as first practice at the Chinese Grand Prix was disrupted by three failures on two separate cars.
Williams’ Felipe Massa suffered two collapsed left-rear tyres and Renault’s Kevin Magnussen a left-rear failure. Both used the ‘soft’ Pirelli tyre.
The session was stopped for nearly half an hour while officials launched an investigation into what had happened.
Williams and Renault could not immediately say what had happened.
Pirelli said the Williams failures were caused by a collapse of the wheel rim.
However, a Williams spokeswoman said: “We had two rim failures but I can’t tell you if they were exactly the same. The engineers are looking into what caused them. Contact from somewhere but not sure how at this stage.”
Pirelli added that it believed a “mechanical failure of some kind” on the car had also caused Magnussen’s problem. Renault could not immediately comment.
The Dane’s left-rear suspension failed and he had a puncture but it is not clear which was the initial cause of the problem.
Both Massa’s failures happened on his first lap out of the pits on the entry to the Turn Six hairpin.
On the first, Massa was pitched into a spin. On the second, he did not lose control, but the tyre appeared to simply pop off the rim.
There were no clear television pictures of the failure on Magnussen’s car.
Williams did not send either of its cars out again when the session was re-started with eight minutes remaining. Magnussen, who had broken rear suspension, was also consigned to the pits.
In a busy final few minutes of running, Rosberg supplanted early pace-setter Hamilton at the top of the times with a lap of one minute 38.037 seconds.
The world champion was 0.146secs behind in the second Mercedes.
Rosberg returned to the pits at the end of the session in “limp-home mode”, his engineer telling him over the radio that he thought there was “an engine issue”.
Hamilton already knows that he has a five-place grid drop from wherever he qualifies because of a gearbox change after the team discovered a potential problem and decided not to risk a retirement.
Ferrari’s Sebastian Vettel was third quickest, 0.628secs off the pace and 0.396secs quicker than Red Bull’s Daniel Ricciardo in fourth.
Ferrari’s Kimi Raikkonen was fifth, ahead of Red Bull’s Daniil Kvyat, Toro Rosso’s Carlos Sainz and the McLaren of Jenson Button.
Fernando Alonso returned to the McLaren after being forced to miss the last race in Bahrain because of a broken rib sustained in his high-speed crash at the season-opening Australian Grand Prix.
The Spaniard faces further medical checks after the first session to establish whether he will be allowed to continue for the rest of the weekend but he made no public reports of any physical discomfort.
Alonso was 12th fastest, 0.564secs slower than Button.
Chinese Grand Prix first practice results
Chinese Grand Prix coverage details