Some debris has been spotted in the seas between Malaysia and Vietnam but it is unclear whether it came from the missing Malaysia Airlines flight MH370, a Chinese official said in Beijing on Sunday.
Mr Li Jiaxiang, chief of Civil Aviation Administration of China, was speaking at the sidelines of the tail-end of China's ongoing National People's Congress (NPC), or its annual national parliament meetings, where thousands of delegates have gathered in the Chinese capital.
"We are still unclear about the exact situation and position of the plane, and hold hope that the passengers are miraculously alive," he said, according to a report by China News.
"It is also unclear at the moment if the plane was involved in a terrorist attack," he added.
The Boeing 777-200 is a "mature plane model" and it is rare for it to have gone missing for more than 30 hours, said Mr Tang Jun, general manager of AVIC Aircraft Corporation, also on the sidelines of the NPC.
"Since we are unable to get any signals from the plane, the likelihood that it might have broken up in pieces mid-flight is high. If so, the main causes could be a thunderstorm or adverse weather conditions or possibly explosives on the plane," he was quoted as saying in the same report.
Meanwhile, state-run Xinhua News Agency said on Sunday that two warships of the Chinese navy, "Jinggangshan" and "Mianyang", are on their way to the area where the missing plane may have crashed.
Chinese Maritime Police 3411, a 4000-tonnne vessel, was on duty in nearby sea areas and could be the first Chinese vessel to arrive on the scene early Sunday afternoon, state media said.
Family members of the flight's passengers are currently staying at Crowne Hotel Beijing Lido, accompanied by about 100 staff from Malaysia Airlines who arrived in the early hours of Sunday morning.
The media has not been informed or any other press conference and the situation has been described as tense as relatives anxiously wait for news with a middle-aged woman, overwhelmed with emotions, fainting at the hotel lobby.