PEOPLE across Swindon have been left wondering what caused a loud explosion at approximately 6.20pm.

Residents have reported loud bangs and walls shaking due to the force, however the cause is not yet know.

Wiltshire Police said they had been inundated with calls but did not know the source. Possible causes included a sonic boom, earth tremor and the weather.

Social networking sites have been flooded with messages and there are reports that the noise was heard as far north as Coventry.