Firefighters were called at around 01.40 pm today after smoke was seen billowing from underground garages at Estela Road, Buckland.
A passer-by heard a loud explosion followed by plumes of smoke billowing from the underground garages.
Crews from Cosham, Portchester and Southsea attended who extinguished the fire in the garage.
A full investigation into the cause of the blaze is now underway.