Peering up through black protective glasses at an overcast sky, Glenn Evans let out an excited cry as the barely visible sun began to disappear completely behind the moon.

"You can see it. It's already started!" Evans, a Shanghai-based cosmetics executive, called out to other eclipse-watchers.

Evans was one of hordes of Shanghai residents and tourists who poured into the Chinese city's streets amid cloudy morning skies and intermittent rain Wednesday, hoping for a clear view of the longest eclipse of the 21st century.

There was disappointment across the eclipse's wide path through India and China, with many barely getting only a glimpse of the once-in-a-lifetime event after traveling around the world.

But despite the brief, soggy views, many were amazed nonetheless by the spectacle of day turning to night for nearly six minutes.

Thousands of tourists had descended on Shanghai for the eclipse, with hotels and restaurants in marquee locations fully booked despite early warnings that visibility would be a problem.

At the M on the Bund restaurant, which marked the event by serving breakfast for the first time, applause broke out as the lunar shadow fell on the city at 9:36 am (0136 GMT), lasting for about six minutes.

"It's so long, this is absolutely long," said Erick Lansard, the head of the orbital mechanics committee at the International Astronautical Federation, who was visiting from Paris.

"When I got on the plane they said the probability of seeing anything was 10 percent maximum, so I was very happy to see the beginning of the eclipse," he said, standing on M on the Bund's rooftop patio.

On the street below, office workers spilled out of buildings as darkness fell.

"It's like magic, the day turns into night in such a short period of time ... I have no idea where I am right now. It feels like a different world," said Chen Hong, a biotech company chief executive.

Shanghai's landmark Oriental Pearl Tower and other skyscrapers across the Huangpu river left their lights off during the eclipse to enhance viewing. Car headlights reflected on the wet streets provided some of the only light.

"It's a very eerie darkness," said Siobhan Das Bachran, a Malaysian businesswoman, who said she had seen a partial eclipse more than a decade ago in Dubai. "It's like twilight."

In eastern India, tens of thousands gathered in the village of Taregna after scientists insisted it would offer the best view of any site in the country, but many were disappointed.

American tourist Shaun Allen, who said he had travelled to India with four friends specifically to see the eclipse, complained that weather conditions had ruined the experience for him.

"It turned out to be a complete waste of time and money," said the 33-year-old Allen.

"The cloud cover was very thick. We could not see anything. I am very upset."

Ram Lakhan Prasad, an Indian civil servant, said Wednesday's eclipse "would have been the experience of a lifetime if it weren't for the clouds".

"We travelled here yesterday and stayed awake all night for a skyful of cloud," he said. "But you can't blame nature. It's monsoon (season) after all."