China's notoriously murky air prevented a full running of the Chinese Grand Prix's practice sessions Friday in a frustrating day for drivers and fans in Shanghai.
Smog and damp weather combined to cut short morning practice and force the cancellation of the afternoon running without title hopefuls Lewis Hamilton and Sebastian Vettel ever laying rubber.
The problem wasn't even at the track -- Formula One said the race's medical helicopter would have been barred from landing at designated hospitals due to Chinese rules on flight visibility.
A local airport in the area even had to be closed, the FIA noted.
Air quality in Shanghai was in the "unhealthy" range, according to readings put out by the US Consulate in the city.
There was no immediate announcement on whether the situation could affect the race schedule, but further poor weather was expected this weekend.
More than half the drivers got a crack at the boggy circuit during a curtailed morning running, with Max Verstappen of Red Bull getting around the quickest.
But the situation delayed the hotly anticipated resumption of hostilities between Mercedes and Ferrari.
Hamilton and defending champions Mercedes have vowed to bounce back after their wake-up call in the season opener in Melbourne two weeks ago, where Vettel steered his Ferrari to a commanding victory.
Forlorn drivers sat in the pits or in their cars Friday as they waited to see whether the afternoon's practice would ever get under way before time eventually ran out.
Drivers will have a final chance at practice on Saturday before afternoon qualifying -- if the air clears up.
Times were slow as teams ran full wets during the short Friday session.
It was treacherous going for Kevin Magnussen of Haas, who spun out twice, and Renault's Nico Hulkenberg beached his car on a gravel embankment and had to abandon it.
Hamilton, a three-time world title winner, recalled the "wheel-to-wheel" battles of his go-cart driving days in saying Thursday that he looked forward to a season-long fight with Vettel.
"I yearn for those kinds of battles," said the Briton. "I'm dying for that day to come again and I hope that happens with me and Sebastian."
Ferrari have shown impressive early pace, with 2007 champion Kimi Raikkonen taking fourth in Australia and signs pointing to another tight battle between the two top teams in China.
Newly introduced wider cars and fatter tyres of 2017 appeared to make overtaking harder in Melbourne, but Shanghai's longer stretches could make for more lead changes.