A big fire at a power plant has left 1.5 million people without electricity in the US territory of Puerto Rico. The fire affected two transmission lines and caused the collapse of the electricity system across the island. Supply is expected to be restored to most areas today. The fire department said it had extinguished the blaze at the power plant in the south of the island, which serves most of the island's 3.5 million people. The cause of the fire is still unclear.