The Gaza Strip's only power station, which supplies the Palestinian enclave with up to two-thirds of its energy needs, was shut down on Tuesday because of a shortage of fuel from neighboring Egypt.
The closure led to widespread blackouts for Gaza's 1.7 million inhabitants. The local power company warned that households would receive only six hours of electricity a day until the problem was resolved.
Gaza's Energy Authority said "measures taken" on the Egyptian side of the border meant not enough fuel was entering the territory.
It did not provide further details. Some local experts said Hamas had mismanaged Gaza's power needs by failing to provide a viable alternative to the precarious tunnels under Gaza's border with Egypt.
The Gaza power plant needs 600,000 liters of fuel a day to keep running, but the Palestinian Center for Human Rights said only 340,000 litres had arrived from Egypt since Friday, with no reserve stocks left in Gaza to cover the shortfall.
"We are sorry to announce that we are unable to provide hospitals, education premises, water pumps and waste water facilities and all other fields of life with the enough quantities of electricity," said Ahmad Abu Al-Amreen, information director at the Energy Authority.
He urged Egypt to allow more fuel into Gaza, but did not explain what had caused the sudden drop in the flows.
Locals said in normal circumstances a fleet of trucks arrived at the Egyptian side of the border and pumped fuel through pipes in the tunnels that lead into Gaza.
Israel closed off its own fuel pipeline into the enclave in January 2010, but limited electricity still reaches the coastal strip through power lines from Israel, bypassing the power station.
Abu Al-Amreen said Israel bore overall responsibility for the ongoing crisis, but Mustafa Ibrahim, a human rights researcher and writer, said Hamas's administration had failed to provide the territory with an energy safety net.
"(The Energy Authority) made everything depend on fuel smuggled through the tunnels, without having any guarantees that this flow could continue. The current severe crisis is evidence that this was the wrong approach," he said.
The sound of generators roared in Gazan streets as businesses tried to keep the lights on, but the PCHR warned that the power cuts could have serious consequences.
"The current crisis may impact access ... to vital services, including the supply of drinking water," it said in a statement.
In 2007, the Israeli and Egyptian closure of Gaza severely restricted fuel supply. Fuel was first smuggled through tunnels from Egypt, then used in electricity generation after a local engineer developed a refining process. The engineer was later abducted by Israeli intelligence agents during a trip to the Ukraine.
Gaza's energy sector is crippled by a ban on importing materials for locally implemented construction, leaving power stations unable to function. The plant suffered damage in Israeli attacks on Gaza in 2008 and 2006.