Beirut, Lebanon (CNN) -- An unintentional fireworks explosion rocked downtown Beirut on Thursday, injuring five civilians who were working with a local non-governmental organization, a Lebanese interior security forces source told CNN. The blast, which occurred around 8 p.m. (1 p.m. ET), left a crater on fire next to Martyr's Square. Those hurt were working with the fireworks for a celebration on Thursday, which is Army Day in Lebanon, when a large firework never launched and instead exploded on the ground, the security forces source said. They'd been working on a grassy area, which is one reason that there was no significant damage to nearby buildings, despite the substantial size of the blast. Ambulance crews and firefighters converges on the scene, the latter trying to put out flames that had spread into the grass. Watch: Fireworks disasters .
An accidental fireworks explosion rocks downtown Beirut . 5 who'd been working with the fireworks are hurt, a security forces source says . A large firework never launched and exploded on the ground, he adds .