Apple gave consumers their first hands-on look at its smartwatch Friday pushing into wearable tech just as rival Samsung rolled out its new flagship smartphones.

With the world's two biggest gadget makers vying for consumer attention, Apple scored points by apparently selling out of the Apple Watch as quickly as it opened pre-orders.

Customers ordering the watch, due to go on sale April 24, saw messages saying deliveries now were being pushed back into June or later.

"I really debated if I should buy the thing," said Eric Angelosanto, one of the customers looking to try the smartwatch at a New York Apple store, who indicated that he had already placed an order online.

"It's tremendously overpriced, but a treat."

The Apple Watch starts at $349, with a limited-edition gold version priced at $12,000.

Angela Ahrendts, Apple's senior vice president of retail and online stores, said she expects "that strong customer demand will exceed our supply at launch.”

Some analysts were not so sure about prospects for the new wearable device.

"The watch's success is anything but guaranteed," said Roger Kay, analyst at Endpoint Technologies Associates.

"Most people I've talked with are not ready to buy one. It seems expensive, redundant and perhaps invasive."

In Paris, at the company's flagship store by the Place de l'Opera journalists outnumbered customers, with Apple encouraging customers to place orders online and with stores offering only demonstrations.

Would-be early buyers queued for a "trial fitting" at the Apple store in Tokyo's chic Omotesando area.

"I'm very keen to buy it," said Kazuki Miura, a 43-year-old technology writer, as he slipped the device onto his wrist.

Apple's device, which connects to the iPhone to facilitate messaging, calls and apps geared toward health and fitness, is a latecomer to the smartwatch market, and follows launches from Samsung, Huawei, Motorola, LG and others including the crowd-funded Pebble watch.

And not only tech companies: last month luxury Swiss watchmaker TAG Heuer announced it was joining forces with Google and Intel to develop a rival to the Apple Watch.

But because of Apple's devoted customer base, analysts expect the new watch to quickly take the lead and sell millions.

Meanwhile, Samsung's Galaxy S6 and its curved-edge variant, the Galaxy S6 Edge, went on sale in South Korea, home of the electronics giant, as well as Europe, the United States and markets in the Asia-Pacific such as Australia, Singapore and India.