Four workers have died and 17 have suffered injuries after scaffolding collapsed at a cathedral in the southern Mexican state of Oaxaca. At least four additional workers remained missing and were presumed buried under debris, according to press reports. The collapse occurred on March 3 in the city of San Juan Bautista Tuxtepec, 275 miles southeast of Mexico City. Civil protection officials were unable to explain what caused the scaffolding - used to support the roof while it is under construction - to collapse and send debris crashing down 70 feet. The Televisa network reported that the workers were on the scaffolding as it fell. Press photos from the scene showed civil protection officials, police and an estimated 2,000 volunteers hauling rubble from the cathedral - which was to be known as "The Ship" because of its unique shape. The Mexican bishops' conference released a statement expressing sadness over the tragedy and offering prayers for the victims and their families. The bishops sent "prayers for the deceased and most heartfelt condolences for their families, to whom we express our solidarity and unconditional support at this time of grief," the Diocese of Tuxtepec said in statement signed by Bishop José González Juárez.