BEIJING (REUTERS) - China has sent an "unbreakable" code from a satellite to the Earth, marking the first time space-to-ground quantum key distribution technology has been realised, state media said on Thursday (Aug 10).

China launched the world's first quantum satellite last August (2016), to help establish "hack proof" communications, a development the Pentagon has called a "notable advance".

The official Xinhua news agency said the latest experiment was published in the journal Nature on Thursday, where reviewers called it a "milestone".

The satellite sent quantum keys to ground stations in China between 645km and 1,200km away at a transmission rate up to 20 orders of magnitude more efficient than an optical fibre, Xinhua cited lead scientist Pan Jianwei on the experiment from the state-run Chinese Academy of Sciences, as saying.

"That, for instance, can meet the demand of making an absolute safe phone call or transmitting a large amount of bank data," Mr Pan said.

Any attempt to eavesdrop on the quantum channel would introduce detectable disturbances to the system, he added. "Once intercepted or measured, the quantum state of the key will change, and the information being intercepted will self-destruct," Xinhua said.

The news agency said there were "enormous prospects" for applying this new generation of communications in defence and finance.

China still lags behind the United States and Russia in space technology, although President Xi Jinping has prioritised advancing its space programme, citing national security and defence.

China insists its space programme is for peaceful purposes, but the US Defence Department has highlighted its increasing space capabilities, saying it was pursuing activities aimed at preventing adversaries from using space-based assets in a crisis.