A government environmental monitoring centre in Shaanxi said on its website that a military facility in the province was developing Dongfeng-41 (DF-41) missiles, the Global Times reported.
The DF-41 is designed to have a range of 12,000 kilometres, according to a report by Jane's Strategic Weapon Systems, putting it among the world's longest-range missiles.
It is "possibly capable of carrying multiple independently targetable re-entry vehicles", the US Defence Department said in a report in June, referring to a payload of several nuclear warheads.
The original government web post appeared to have been deleted today, but the newspaper posted a screengrab.
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It also quoted a Chinese military analyst as saying: "As the US continues to strengthen its missile defence system, developing third generation nuclear weapons capable of carrying multiple warheads is the trend."
China's defence ministry in January responded to reports that it had tested a hypersonic missile delivery vehicle by saying that any military experiments were "not targeted at any country and at any specific goals".
Tensions between Washington and Beijing have risen in recent months over territorial disputes with US allies in the East and South China Seas, and cyber-hacking.
Beijing has boosted its military spending by double digit amounts for several years as it seeks to modernise its armed forces, and now has the world's second biggest military outlays after the US.
Chinese President Xi Jinping said last month that any confrontation between the two powers "will surely spell disaster for both countries and for the world".
The DF-5A had its first test flight in 1971, and has to be fuelled for around two hours prior to firing, limiting its effectiveness as a weapon, according to analysts.