Gaza officials said Saturday that they switched off all three turbines that had been generating electricity for hundreds of thousands of Gazans.
Energy official Kaanan Obeid said Israel hadn't provided enough diesel to run the power plant.
Ninety percent of Gaza City was plunged in darkness Saturday night, Obeid said.
Israel has limited its rations of fuel and other supplies to Gaza in an attempt to pressure terrorists to stop firing rockets at the western Negev.
An IDF spokesman said Saturday that Israel didn't deliver as much fuel as planned to Gaza this week because Palestinian terrorists attacked the crossing used to deliver it. He said he did not know when fuel supplies to the power plant would resume.
The plant has shut down before, citing fuel shortages, but Israel delivered fuel the following day.
It was not immediately clear if the privately owned power station had actually run out of fuel Saturday or whether it was shut down to pressure Israel to deliver fuel.
Government spokesman David Baker denied Israel was to blame for the blackout.
"Israel continues to supply fuel and vital humanitarian goods to Gaza," Baker said. "There is no logical reason for this fuel plant to be shut down. This is another example of Hamas orchestrating an artificial crisis for its own political aims and once again Hamas is showing a complete disregard for the welfare of the Palestinian people."
Earlier Saturday, Egyptian authorities ordered a three-day opening of the Rafah border crossing on Saturday to allow Palestinians to cross into Egypt from the Gaza Strip for medical treatment, said a security official at the terminal.
Palestinians in urgent need of surgery as well as cancer and heart patients will be given priority to cross into Egypt, the official said, speaking on condition of anonymity because he was not authorized to speak to the press.
On Friday, Hamas leader in exile Khaled Mashaal urged Egypt to open Rafah crossing if Israel rejected its truce proposal, Hamas and other Palestinian factions endorsed the proposal in principle in late April.
Hamas is trying to negotiate a new arrangement for the border crossings with Israel and Egypt, as part of a wider package that would also include a Gaza-Israel cease-fire and a prisoner swap.
Speaking in Damascus, Mashaal said that Egypt should open the terminal even if Israel rejects the truce.
"If Israel rejects this Egyptian effort," Mashaal said, "I demand Egypt and Arab countries to immediately take the unilateral initiative to lift the siege and open the Rafah crossing."
"No Arab has an excuse not to do that," he said, vowing to take "creative" measures.
