The craft took off from the US Army’s Yuma Proving Ground in Arizona at 1440 BST (0640 local time) last Friday and is still in the air.
Its non-stop operation, day and night, means it has now gone five times longer than the official mark recognised by the world air sports federation.
The plane has been developed by the defence and research company Qinetiq.
Its project manager, Jon Saltmarsh, said Zephyr would be brought down once it had flown non-stop for a fortnight.
“Zephyr is basically the first ‘eternal aircraft’,” he told BBC News.
The UAV has been under development for a number of years at Qinetiq.
Solar-powered high-altitude long-endurance (Hale) UAVs are expected to have a wide range of applications in the future.
The military will want to use them as reconnaissance and communications platforms. Civilian and scientific programmes will equip them with small payloads for Earth observation duties. Read at…