PENGHU, Taiwan ? A Boeing 747-200 that China Airlines planned to retire next month broke apart mid-air and crashed Saturday in the Taiwan Strait as it was flying 225 people to Hong Kong. Searchers who looked through the night and into Sunday found 31 bodies but no survivors.

Rough seas slowed the search today for bodies and debris from Flight CI611, which China Airlines said had sent no distress signals before it dropped off radar screens. The plane vanished about 20 minutes after taking off on a clear afternoon.

“Communications had been normal,” said James L.S. Chang, a China Airlines vice president. “The light spot suddenly disappeared from radar.”

Swells up to 10 feet high battered fishing boats and coast guard ships that were scanning the waters around the crash site, north of the Taiwanese island chain of Penghu, about 30 miles off Taiwan’s west coast.

Officials said they did not know what caused the Boeing 747-200 to crash. Tsai Duei, a vice transportation minister, told reporters that the plane broke apart in the sky, but he said officials could not say if an explosion caused the accident.

There were early suspicions that the plane might have exploded in flight because farmers in the west coast county of Changhua near the plane’s flight path were finding scraps of airline magazines, immigration forms and other papers with China Airlines stickers or labels on them. TVBS cable news showed officials wading into rice fields with flashlights collecting the bits of paper and putting them in plastic bags.

Chang would not speculate on what caused the crash, but told reporters the accident seemed highly unusual.

“At such a high altitude, 35,000 feet, to have something go wrong and the pilot didn’t even have time to send a distress signal. Now, that’s a big question mark,” Chang said.

Near the crash site Sunday morning, the smell of fuel was thick in the air and there was a rainbow-colored glimmer on the sea from an oil slick as big as a football field.

Rescue officials said 31 bodies have been found. The passengers included 190 Taiwanese, 14 people from Macau and Hong Kong, one Singaporean and one Swiss citizen.

Losing the plane is a serious blow for China Airlines, which is trying to shed a reputation for being one of the world’s most dangerous airlines. In the past five years, Taiwan’s largest carrier has been aggressively retraining pilots and revamping its safety procedures.

The Boeing 747-200 had been flying for 22 years, and China Airlines planned to retire the jetliner next month. However, the airline has argued the aircraft was safe and had been completely overhauled last year.

Several fishing boats that were searching for bodies Sunday morning decided to return to port because they weren’t finding anything.

At Taipei’s international airport, some victims’ families suspected that the crash was caused by the plane’s age. The airline had been using the Boeing 747-200 for 22 years.

“Why did they put this old plane in service? Did they want people to die?” asked El-Hinn Ibrahim, who had two sisters-in-law and one brother-in-law on the flight.

Larry McCracken, vice president of public relations for Boeing, said the age of the plane would not be a factor by itself.

“Life spans are 30-40 years,” he said. “It depends on how much they’re used and how they’re maintained. “There are 707s and DC-8s flying around that were built in the 50s,” he said.