A power outage on New Year's Eve plunged much of Puerto Rico into darkness.RICARDO ARDUENGO/AFP via Getty ImagesA massive blackout in Puerto Rico left more than 1.3 million power company customers in the dark.Luma Energy, the power company, said restoring power could take up to 48 hours.It said that the outage appears to have been caused by the failure of an underground power line.A massive blackout hit Puerto Rico early Tuesday morning — and it could take days to restore power.The outage, which struck around dawn, the Associated Press reported, left nearly 90% of private power company Luma Energy's 1.47 million customers without power, the company told the AP.Luma said the issue appeared to have stemmed from the failure of an underground cable.