Apple says its first wearable device will connect wirelessly to a user's iPhone and will be the interface for messaging, calls and apps, especially ones geared toward health and fitness.
"I'm very keen to buy it," said Kazuki Miura, a 43-year-old technology writer, after slipping the device onto his wrist.
Apple began taking orders at its Tokyo store in the morning, and was set to start global online reservations at 0701 GMT. First deliveries will begin in nine countries on April 24.
Dozens of customers had waited outside the Apple store in Omotesando for several hours before being ushered down into the basement one-by-one for what Apple called their trial fitting.
Users can also send a real-time display of their heartbeat to another Apple Watch.
Miura's colleague Hisanori Kogure, 35, joked to him "I'll send you my pulse", to which Miura replied: "No, thank you."
IT worker Ahi To, 24, had dropped in at the Apple shop to see "the newest gadget" on his way to work and said he was taken by the possibility of wirelessly connecting it to an iPhone.
Prices will start at $349 (roughly Rs. 21,000), with a limited-edition gold version costing $10,000 (roughly Rs. 6 lakhs).
Tech firms are betting heavily on wearables as the next frontier in consumer electronics, with offerings from Motorola and Samsung, amongst others, joining the fray.
Luxury Swiss watchmaker TAG Heuer announced last month it was joining forces with Google and Intel to develop a rival to the Apple Watch.
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