A Thai diesel oil tanker with 14 crew members en route from Singapore to Indonesia is believed to have been hijacked, the International Maritime Bureau (IMB) said on Saturday, the second major case in months on one of the world's busiest waterways. "It could be a hijacking. We have sent signals for ships in the area to keep a lookout and the authorities have been alerted," Noel Choong, the head of IMB's Kuala Lumpur-based Piracy Reporting Center, told Reuters on Saturday. Authorities lost contact with the MT Orapin 4 after it departed from a terminal in Singapore on May 27, according to a report by the IMB. It was headed for Pontianak, Indonesia.