A powerful typhoon roared toward China's southern coast, forcing the evacuation of more than half a million people and the cancellation of dozens of flights, the government said Thursday.

Typhoon Chanchu's eye was picking up speed and was expected to hit Guangdong province, one of China's biggest manufacturing centers, later in the day, the official Xinhua News Agency said.

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Some 327,000 coastal Guangdong residents had already been moved inland Wednesday and more than 51,000 ships were ordered to return to harbor, Xinhua said.

In Fujian province, just north of Guangdong, more than 307,000 people were evacuated and 42,000 ships were docked, it said.

Some 26 — mainly domestic — flights out of Fujian were also were canceled and Shanghai-based China Eastern Airlines canceled 38 flights headed for Hong Kong the nearby mainland city of Shenzhen, it said.

After slamming into Guangdong, Chanchu was expected to churn up the coast to Fujian province, just across from Taiwan, according to the Hong Kong Observatory's forecast and tracking map.

The storm was picking up speed as it moved 15 mph with winds of 98 mph near its center.

As the storm churned through the South China Sea, it caused an oil tanker to run aground near Taiwan's southern port of Kaohsiung, officials said. Rescuers in helicopters lifted 13 crew members off the ship.

The typhoon, the strongest ever reported in the South China Sea in May, was heading toward Hong Kong earlier this week, but it changed course overnight, swirling about 140 miles east of the city on Wednesday afternoon. The storm kicked up high waves and spawned showers but caused no major damage.

In southern Japan, high waves swept three 17-year-old male students from near a beach on Wednesday afternoon, leaving one dead and another missing, officials said.

They were in the water off Hateruma island in the southern island chain of Okinawa when high waves swept them out to sea, according to coast guard spokesman Shoji Kawabata.

One was found floating near the island and later pronounced dead at a hospital, Kawabata said. Another was rescued by a local diving boat, while the third remained missing.

Chanchu swept over the Philippines last weekend, killing 37 people and destroying thousands of homes.