New Delhi, July 15 -- HAVANA - The power went out across Cuba for the third time in two weeks on Tuesday, the island's largest energy emergency entering a phase that its grid operators appear increasingly unable to contain. A malfunction in a single generating unit in Holguin province triggered a sudden frequency change that collapsed the National Electric System around midday, state officials said, leaving the entire island without electricity in the middle of the afternoon. Nine million people lost power simultaneously.

small pockets of generating capacity brought up separately, then gradually reconnected, with hospitals and food processing facilities receiving power first. By late afternoon, roughly 4 percent of Havana had electricity...