The United States and other countries will be welcome to use civilian facilities that China is building in the South China Sea for search and rescue and weather forecasting "when conditions are right", the PLA navy chief has told a senior American officer. China claims 90 per cent of the South China Sea, which is believed to be rich in oil and gas, with overlapping claims from Brunei, Malaysia, the Philippines, Vietnam and Taipei. Recent satellite images show China has made rapid progress in building an airstrip suitable for military use in the disputed Spratly Islands and may be planning another. Those moves, along with other reclamations, have caused alarm around the region and in Washington too, with the issue dominating a summit of Southeast Asian leaders this week, to China's displeasure. In a teleconference with the US Chief of Naval Operations Jonathan Greenert, PLA Navy chief Wu Shengli said China's building work in the South China Sea would not affect freedom of navigation or overflight. "Instead, it will improve the ability in these seas of public services like weather forecasting and maritime search and rescue, fulfilling international obligations to maintain the security of international seas," Wu said, according to a defence ministry statement. "[We] welcome international organisations, the United States and relevant countries to use these facilities in the future when conditions are right, to have co-operation on humanitarian search and rescue and disaster relief," Wu added. The statement cited Greenert as saying he hoped China could explain in a timely manner the aim of the building work. It would also be good for maintaining stability and freedom of navigation if other countries could use such facilities for joint humanitarian operations, he said. Disputes over how to tackle an increasingly assertive stance by China, an ally of several Southeast Asian states, in the strategic South China Sea make the issue the region's biggest potential military flashpoint. China this week accused Vietnam, the Philippines and others of carrying out their own illegal building work. Analysts said sharing use of facilities could ease tension in the region. "By offering to open those facilities for civilian use in the future, the PLA hopes to ease agitation over our construction in the South China Sea islands," said Ni Lexiong , a Shanghai-based military affairs commentator. "Compared with what the PLA has always said - that the Spratlys belong to China and no one else can meddle in our affairs - it is a more moderate and diplomatic way of making our claim." Beijing wanted to demonstrate its strength in the area, but not push too much to infuriate other countries, he said. Veteran military officer Yue Gang said the offer could serve as a reasonable justification for what the PLA has built in the South China Sea. "It also indicates China is confident that by sharing the facilities for peaceful use, it can still have them under its control," Yue said. He said the teleconference was the first between the head of the Chinese and US navies, and indicated the US hoped to avoid accidental clashes arising from a lack of communication.