Darmstadt: Skywatchers will need sharp eyes and a lot of luck to catch a glimpse of China’s Tiangong-1 space lab when it falls to Earth this weekend, a space expert said on Thursday.

The craft is expected to re-enter Earth’s atmosphere on Saturday or Sunday, but no one knows for sure where it will come down, Holger Krag, head of European Space Agency’s Space Debris Office, told Reuters TV.

‘It is very rare to see something like this,’ he said.

‘It is the upper atmosphere that will create a drag that will eventually bring down the station. That drag is very, very hard to understand and to predict,’ he said.

Anyone lucky enough to be looking at the right part of the sky when Tiangong-1 starts its fiery descent will likely see a glowing object moving for several minutes, like a shooting star but slower.

The craft is expected to hit speeds of 27,000 km (16,777 miles) per hour and partly burn up during re-entry. The rest will break up into fragments that could cover thousands of square kilometres, though the risk to people will be very small, experts promise.

‘There have been 13,000 tonnes of space hardware coming down in the whole history of space flight and there has not been a single casualty reported,’ Krag said.

The 10.4-metre-long (34.1-foot) Tiangong-1, or ‘Heavenly Palace 1’, China’s first space lab, was launched into orbit in 2011 to carry out docking and orbit experiments as part of China’s ambitious space programme, which aims to place a permanent station in orbit by 2023.

It was originally set to be decommissioned in 2013 but China has repeatedly extended the length of its mission, leading some scientists to believe that it has gone out of control.

It will come down somewhere between the 43^rd north and south parallels, roughly between the latitudes of London in Britain and Wellington in New Zealand, but it is impossible to be any more specific, ESA’s Krag said.

Advancing China’s space programme is a priority for President Xi Jinping, who has called for Beijing to become a global space power with both advanced civilian space flight and capabilities that strengthen national security.