In a warning issued on Friday morning, the bureau’s Australian Space Weather Forecasting Centre said a level G4 storm – the second-highest classification – was set to impact from roughly 8pm on Friday and weaken through the weekend.

“The warning issued for this event informs government and critical infrastructure operators so they can take action to mitigate potential impacts on infrastructure assets and essential service,” the BoM said.

Forecasters warned the storm had the potential to disrupt “critical infrastructure such as power grids, causing power outages” and “satellite services, affecting communications and global position, navigation and timing services that use high-frequency radio communication”.

A power outage in Sydney left thousands in Newtown without power for hours on Friday night but it was unclear if there was any link to the solar activity.

Bright auroras would be visible at unusually low latitudes, including dark areas near Sydney and Perth, if G4 conditions were reached, the bureau said.

Conditions are expected to reduce to G3 on Saturday and continue until about 6am on Sunday, plus or minus about 10 hours.

“The G-scale is a measure of global geomagnetic activity, which refers to fluctuations in Earth’s magnetic field across the globe. The G-scale ranges from G1 (minor) to G5 (extreme),” the bureau said.

It’s caused by at least four mass ejections from the sun, which took place from Wednesday afternoon until Thursday night.

In the United States, the National Oceanic and Atmospheric Administration issued a similar warning, saying it was the first G4 watch since 2005.

“Several strong flares have been observed over the past few days and were associated with a large and magnetically complex sunspot cluster … , which is 16 times the diameter of Earth,” the forecaster’s space weather centre said.

It described the ejections as “explosions of plasma and magnetic fields from the sun’s corona”.

NASA shared colourised videos of two flares ejected from the sun on Wednesday with a similar warning about the potential for disruption.

“The Sun—like even the most vibrant people—is not a constant ray of sunshine,” the space agency said.

“It constantly cycles through periods of higher and lower activity. High activity can lead to these solar flares, or dramatic explosions of energy out from the Sun.”