According to this site, this event occurs on the Greek island of Chios during Easter:
The Rocket War of Vrondados is an old custom that began at the time of the Turkish occupation and it still happens every year at Easter. In the beginning the residents of the parishes of Panagia Erithiani and Saint Mark's, which are facing each other, made small cannons, to fire at each other. But through time the canons became rockets and fireworks made from nitre, sulphur and gunpowder.
The preparation of the rockets starts immediately after each Easter, so everything can be ready for the next year. Each year the amount of the rockets increases and the fireworks burning in the air, at the night of the Christ's resurrection, are really magnificent. Many people visit Chios Island this time of the year, so they can enjoy this truly unique but dangerous event. For this reason, the last few years measures are taken for the protection of all the people that participate in this event and the surrounding houses, so the custom can be continued safely.
Must be a tough job being a fireman during Easter on that island.