A panel of aerospace experts will select the two astronauts for China's second manned space mission today - just a day before the Shenzhou VI is launched. Tan Zhenya , the Communist Party secretary of the Nanjing University of Aeronautics and Astronautics, was quoted by the Modern Times newspaper based in Nanjing as saying that the liftoff from the Jiuquan space centre in Gansu province was scheduled for 9.30am tomorrow, a day earlier than planned. Mr Tan is one of the guests invited to witness the launch. The semi-official China News Agency confirmed the change of liftoff date, quoting sources at the space centre. But the agency said the launch could be postponed if the weather turned bad. Earlier reports said a strong cold air mass would be affecting the region between tomorrow and Friday, the scheduled launch window. The China National Space Administration in Beijing will not confirm the date of the launch, which has been shrouded in secrecy. The China News Agency said Nie Haisheng and Fei Junlong , two of the six shortlisted astronauts, were tipped to carry out the mission. The agency said relevant experts would cast their vote today to decide who could become the country's second and third astronauts after Yang Liwei , who made history two years ago with the success of Shenzhou V. Zhai Zhigang , another hopeful among the six shortlisted for the mission, was likely to be left out, it said. The six candidates for the 119-hour space mission, who were grouped into three teams of two, have arrived at the launch site. The two astronauts chosen will be expected to conduct a large number of tests in the spacecraft's orbital module, many of them designed to check their physical reactions to conditions in space. They will return to Earth next week, landing in Inner Mongolia . Security has been tightened around the site, with traffic leading to the centre cut off since yesterday. No cars or civilians were allowed to pass through a checkpoint 30km from the centre on the only road from Jiuquan city to the site, the Chongqing Morning Post reported. Strict limits have been imposed on the media covering the event, with overseas media, including reporters from Hong Kong, barred from the site. Mainland journalists who had gained access to the site were ordered not to access the internet via wireless devices, or use mobile phones, especially those with cameras, the Chongqing-based newspaper reported.