BRASILIA, Brazil—A towering slab of rock broke from a cliff and toppled onto pleasure boaters drifting near a waterfall on a Brazilian lake on Saturday and officials said at least five people died. Minas Gerais Fire Department Commander Edgard Estevo told a news conference that in addition to the dead, as many as 20 people may be missing, and said officials are seeking to identify them. Officials earlier said at least 32 people were also injured, though most had been released from hospitals by Saturday evening. Video images showed a gathering of small boats moving slowly near the sheer rock cliff on Furnas Lake when a fissure appeared in the rock and a huge piece toppled directly onto at least two of the vessels. Estevo said the accident occurred between the towns of Sao Jose da Barra and Capitolio, from which the boats had left. The press office of Minas …