The sunspot soon grew to be the largest active region observed in the current solar cycle - a periodic change in the Sun's activity and appearance - which began in 2008.
This is the fourth substantial X-class flare from this active region since Oct 19.
"The sunspot region is about 80,000 miles across, which is wide enough for 10 Earths to be laid across its diameter," NASA said in a statement.
X-class denotes the most intense flares, while the number provides more information about its strength.
Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground.
These can also disturb the atmosphere in the layer where GPS and communications signals travel.