Malaysia Airlines Flight 370 could not just "disappear", a Chinese military radar expert said yesterday, and asked whether Vietnamese authorities were withholding crucial information or if staff had "neglected their duty". The aircraft, a Boeing 777-200ER, had reached cruising altitude of more than 10,000 metres when it vanished over the sea between Vietnam and Malaysia, Vietnamese air traffic controllers said. "This is very strange," the expert said. "Radar technology today is so advanced, even a piece of debris just a metre or two long can be detected easily." Vietnamese air traffic controllers should have been able to track precisely the whereabouts of the aircraft and reproduce its flight route, said the source, who declined to be named. Even if the aircraft broke apart in an explosion, the cloud and trajectory of its debris would still leave a trace on a radar screen. "The plane was flying at a very high altitude. The crew had lots of time to use the emergency radio frequency for help. I find it difficult to believe that the Vietnamese did not detect anything, although some staff might have neglected their duty or were not doing their job properly," he said. The expert added that the area where the plane went missing was very busy and closely monitored by ground radar networks. Some passengers might have survived a crash at sea, waiting for rescuers to arrive, the source said. "The rescue efforts have been unreasonably slow," he said. "If there were survivors, whether or not they lived was determined by the speed of the search and rescue operation." In a meeting with the Malaysian chargé d'affaires to China, Bala Chandran Tharman, and Vietnamese ambassador to China Nguyen Van Tho, Deputy Foreign Minister Xie Hangsheng called on both countries to try their best with rescue work, and to inform the Chinese passengers' relatives about the latest developments. Xinhua reported that both envoys said they planned to work closely with China and do their best to help facilitate a rescue. If the plane's black box can be found, investigators should examine whether there was any delay in the rescue operations, according to the radar expert. "Radars have no blind spot on the ocean. After an accident, radar data should provide a fairly accurate estimate on the plane's final location," he said. "There has been very little transparency with the information. This is murder to survivors," he added.