Formula 1 has cancelled all activities at the Japanese Grand Prix on Saturday as Typhoon Hagibis approaches.
The tropical storm, the year's biggest, is due to hit Japan on Saturday and strong winds are set to continue into Sunday, when qualifying and race will be held.
Valtteri Bottas led Lewis Hamilton to a Mercedes one-two in second practice.
Those results could decide the grid if conditions are too difficult to hold qualifying on Sunday morning.
Bottas was 0.1 seconds quicker than Hamilton, with Max Verstappen third and the Ferraris of Charles Leclerc and Sebastian Vettel fourth and fifth ahead of Red Bull's Alexander Albon.
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Organisers said they had taken the decision to postpone qualifying and close the circuit on Saturday "in the interests of safety for the spectators, competitors, and everyone at the Suzuka Circuit".
Qualifying, which had been due to take place at 15:00 local time (08:00 BST) on Saturday, is now due to take place at 10:00 (02:00 BST) on Sunday.
The race will be held as scheduled at 14:10 (06:10 BST).
The potential impact of the tropical storm has already led to the cancellation of two matches at the Rugby World Cup.
F1 organisers delayed a decision on Thursday to have a clearer idea of the path of the storm.
Mercedes were first and second, with Bottas ahead of Hamilton, in both practice sessions.
And the second session took on more importance than normal because teams were aware it could set the grid.
Suzuka is expected to be hit by high winds and heavy rain throughout Saturday in what is currently a Category Three typhoon and is due to hit the coast not far from the track on Saturday before moving north towards Tokyo.
Flights are being cancelled across the country, as are train services from Tokyo to Nagoya, the closest big city to Suzuka, from Saturday morning, as well as most trains between Nagoya and Osaka to the west.
Efforts were being made to limit the potential damage at the track on Saturday, for which there have been warnings to stay inside and Japanese authorities have set up social media accounts and an app for safety tips during the storm.
But, even though the storm has weakened slightly from its high point earlier in the week, there are concerns among officials that the damage might be too extensive for the track to be cleared in time to run qualifying on Sunday morning.
Mercedes find the speed
Mercedes appear to be in a strong position after Friday practice, their cars quicker than anything else on both short runs and longer ones aimed at simulating the race.
In fact, Mercedes were as much as a second a lap on average quicker than Ferrari on their race simulations.
Ferrari, who have won three of the last four races and taken pole position at all of them, appear to have slipped back judging from Friday.
Leclerc was 0.356secs off the pace, with Vettel 0.235secs further behind him, and that was despite the Italian team running their session differently than Mercedes and in a way that should in theory have given them greater potential for a quick time.
All teams took advantage of the lack of running on Saturday to do an extra low-fuel, high-speed run in second practice, but while Mercedes and Red Bull did both their quick laps in the middle of the session, Ferrari did one then and then one at the end.
That was the lap that vaulted Leclerc up from sixth to fourth, but although Vettel was able to improve his personal best lap time, he slipped behind his team-mate.
Albon was 0.336secs off Verstappen, a strong effort from the Anglo-Thai rookie on his first visit to Suzuka and in only his fifth race for the team following his mid-season promotion.
Mercedes have an aerodynamic upgrade on the car that the team hope will wrest back the advantage from Ferrari, while Red Bull also have tweaked aerodynamics as well as a new fuel for their Honda engine aimed at boosting performance on the Japanese manufacturer's home track.
Bottas said: "Very positive day, tried some things. Felt good from the beginning, really happy with the car in general, still minor things with the balance to tweak but both short and long runs felt good. It's always so much fun here driving these cars, and especially when the car feels good.
"It is only practice but I do feel still the gains we've made with the car. We can just push the car further than before. But still Sunday is going to be close.
Hamilton added: "It's a work in progress. When you're first on the track, you're pushing the limits, there is always time to find at this track, always areas you're weak at.
"This is not my strongest of circuits. Valtteri got a massive tow on his fastest lap and gained like 0.5secs up the back straight so it's an interesting dynamic because you don't want to be behind someone in the first part because you need clear air but if you're lucky and you get a slipstream later on, then it's perfect."
Best of the rest was McLaren's Carlos Sainz, ahead of Racing Point's Sergio Perez, Toro Rosso's Pierre Gasly and the second McLaren of Lando Norris.
In the first session, Japanese Naoki Yamamoto was driving Gasly's Toro Rosso on his first experience of F1 and was a creditable 17th fastest.
Yamamoto was just 0.1secs off team-mate Daniil Kvyat but was running the soft tyre while the Russian was on the medium.