A small explosion was heard in the centre of the Bahraini capital Manama on Sunday, three witnesses said, though the cause was not immediately clear.
Police blocked off the road where the incident took place near a government security building in the Adliya district, and a security source at the scene said a car had been damaged by fire. The source did not elaborate and there were no reports of casualties.
The incident took place as the small island kingdom hosted a Formula One Grand Prix, staged about 20 miles south of Manama at the Sakhir desert circuit.
Small bomb explosions occur sporadically in the US-allied monarchy, which has witnessed low-level political unrest since 2011 when the Shi'ite Muslim-led opposition organised demonstrations demanding democratic reforms in the Sunni-led government.