He said that reserves of industrial-grade fuel had dwindled to 400,000 litres since Israel halted fuel deliveries.
But the Israeli military said on Wednesday that the diesel was being pumped to Gaza. One million litres is enough to power the plant for at least three days.
The plant supplies one-third of the territory's electricity, and Israel's electricity utility supplies most of the rest.
Israel cut off supplies after Palestinian fighters attacked the territory's main fuel terminal on Thursday.
The Israeli army's co-ordinating office and the private Israeli company charged with supplying fuel to Gaza declined to comment on the cuts in supply.
Rafiq Maleha, director of the Gaza Power Station, told Al Jazeera on Tuesday that fuel had not entered Gaza for five days.
The Gisha Legal Centre, an Israeli human rights group, on Tuesday wrote to the Israeli attorney general warning that the cuts "violate the state's commitment to the supreme court to permit a minimum amount of fuel to enter Gaza".