China's defunct space station is likely to plunge to Earth early this week, two hours ahead of the originally expected time, South Korean space authorities said Sunday.

The Tiangong-1 will fall to Earth between 9:12 a.m. and 1:12 p.m. Monday (Korean time), the state-run Korea Astronomy and Space Science Institute said, updating its early Sunday calculation of between 7:26 a.m. and 3:26 p.m. Monday.

The 10.5-meter, 8.5-ton decommissioned spacecraft was orbiting the planet at an altitude of 155 kilometers as of 4 p.m. Its orbit dropped 18.8 kilometers from the previous day.

South Korea is among the possible places where its debris could land, along with other Asian and African countries and the Pacific and South Atlantic oceans.

The institute said it will announce whether South Korea is among the possible crash sites two hours ahead of the plunge.

The estimates are still highly variable.

The European Space Agency (ESA) also made similar projections, saying the Tiangong-1 will re-enter the Earth's atmosphere on Monday.

The Ministry of Science and ICT issued an alert Friday, though its return is unlikely to cause any damage. Most of the vehicle is expected to burn up in the atmosphere, but fragments could hit the Earth's surface, the ministry said.

Chinese authorities have said its re-entry will offer a "splendid" show akin to a meteor shower.

The Tiangong-1, launched in 2011, is China's first space station and served as an experimental platform for the country's ambitious space program. (Yonhap)