The Sun has unleashed its strongest flare in four years, observers say.

The eruption is a so-called X-flare, the strongest type; such flares can affect communications on Earth.

Nasa's Solar Dynamics Observatory (SDO) spacecraft recorded an intense flash of extreme ultraviolet radiation emanating from a sunspot.

The British Geological Survey (BGS) has issued a geomagnetic storm warning, and says observers might be able to see aurorae from the northern UK.

The monster flare was recorded at 0156 GMT on 15 February and directed at the Earth. According to the US space agency, the source of this activity - sunspot 1158 - is growing rapidly.

Solar flares are caused by the sudden release of magnetic energy stored in the Sun's atmosphere. [ BBC NEWS ]