Pirates released a Vietnamese oil tanker and its 18 crew members yesterday after siphoning part of its diesel cargo, according to the coast guard.

The Sunrise 689, which left Singapore on Oct. 3 before vanishing from radar for five days, was about 70 nautical miles from Hon Khoai off Vietnam’s southern province of Kien Giang, said Dao Van Quang, chairman and chief executive officer of Hai Phong Sea Product Shipbuilding Co., the registered owner. It’s expected to reach Phu Quoc island today, said Rear Admiral Ngo Ngoc Thu, Vietnam Coast Guard’s vice commander.

“The Southeast Asia waters have never been secure for ships,” Thu said by phone. “In particular, the waters bordering Vietnam and Malaysia are not safe. Although all countries in the region have tried to keep them safe, hijackings still happen.”

Ship hijackings are rising in Southeast Asia, with at least six cases of coastal seizing of cargoes since April, the International Maritime Bureau’s piracy reporting center in Kuala Lumpur said in July. The region includes the Malacca Strait, one of the world’s “most strategic choke points,” according to the U.S. Energy Information Administration.

The Sunrise 689 was scheduled to arrive Oct. 8 in the central province of Quang Tri, Quang said yesterday. It was transporting 5,200 metric tons of diesel, with an estimated value of $4 million, for a Singapore customer, he said.

The hijackers appeared to speak Indonesia’s Bahasa language, Thu said, citing the tanker’s crew. They boarded shortly after it departed Singapore, coming alongside before swarming its decks, beating two pilots and breaking one of the men’s legs.

They also removed 1,400 tons of diesel by pumping the fuel out of two holds into their smaller craft, according to Thu. The ship’s communications and GPS systems were destroyed, and all of the crew’s mobile phones except one were taken.

“I cannot estimate the loss until we see the hijacked vessel, since everything is like a mess now,” Quang said in a phone interview.

To contact the reporters on this story: John Boudreau in Hanoi at jboudreau3@bloomberg.net; Mai Ngoc Chau in Ho Chi Minh City at cmai9@bloomberg.net

To contact the editors responsible for this story: K. Oanh Ha at oha3@bloomberg.net Yee Kai Pin, Mike Anderson