A blast of electrically charged particles from a solar flare is aimed at earth and could disrupt power grids, radio transmissions and orbiting satellites in the coming days.
The origin of the extreme X-flare is the sunspot region in the middle of the sun and is known as AR2158, reports NBC News.
It is strong enough to cause a wide-area blackout of radio frequency communication.
X-flares are among the strongest of solar flares. While there were similar flares in June, they were not directed towards earth.
Solar storms happen often, especially during peaks in the solar cycle and do not directly harm people. They can produce the spectacular northern lights in the sky.
Forecasters do not yet know when Wednesday's solar storm will arrive on earth or which part will bear the brunt. It can arrive on Thursday or take a few days more.