An extreme geomagnetic storm was observed early Saturday morning, the most powerful occurring in nearly 20 years, a meteorological expert said.

"China's National Center for Space Weather announced its first watch of a G5 geomagnetic storm — the strongest rating on scale from G1 to G5 — early Saturday morning since 2006," said Chen Anqin, chief forecaster of China's National Center for Space Weather on Saturday.

A G4 storm was observed at 11 pm on Friday (Beijing time), and it then upgraded to G5 and lasted from 5 am through 11 am on Saturday, Chen said.

"Since Wednesday, multiple moderate and strong solar flares were associated with coronal mass ejections. This has disturbed the Earth's magnetic field and resulted in this round of geomagnetic storms," she said, adding that there is a high possibility of more G3 storms, G4 storms or even G5 storms in the coming days.

Sudden ionospheric disturbances were observed in parts of China in the past 24 hours, the center said.

Some netizens shared online the strong aurora they saw in Altay, situated in the northern part of Northwest China's Xinjiang Uygur autonomous region.

The center issued a red alert on geomagnetic storm at 9 am on Saturday, the highest in its warning system, predicting more occurrence in the following days and cautioning about the impact of the storms on short-wave communication, navigation systems and in-orbit satellites.