- Operators of the sole power plant in the impoverished strip - which relies on Israeli fuel imports - say it will be forced to close in three days.
- "These treatments are undoubtedly being delayed and potentially leading to deaths because of the delays now," he added.
Five days into the worst fighting in months between Israel and militant groups in Gaza, concern is mounting about the humanitarian situation in the Palestinian territory.
It is estimated that more than 200 patients, mostly with cancer, are unable to leave for urgently needed treatment. They include children.
Israel controls two crossings with Gaza - used for people and goods - which have been closed since the start of its military operation on Tuesday.
Operators of the sole power plant in the impoverished strip - which relies on Israeli fuel imports - say it will be forced to close in three days.
A spokesman told the BBC this would "lead to an exacerbation of the humanitarian problems". The plant supplies about half of the electricity in the territory, where some 2.3 million Palestinians live.
A British surgeon who is among an estimated 140 humanitarian workers currently stranded in Gaza says cancer patients are facing potentially life-threatening delays.
Prof Nick Maynard, a consultant surgeon at Oxford University Hospitals, arrived in Gaza City last week as part of an aid programme teaching advanced cancer surgery to Palestinian doctors.
"The doctors I work with here have got multiple examples of people who are in desperate need of cancer treatment," Prof Maynard told the BBC.
"These treatments are undoubtedly being delayed and potentially leading to deaths because of the delays now," he added.
Prof Maynard said he was one of about a dozen non-resident British nationals stuck in Gaza.
Ziyad al-Za'noun, 70, has cancer of the spinal cord and is treated every week at Istishari Hospital in Ramallah, in the occupied West Bank.
"I have been suffering from cancer for three years and there is no treatment for it here in Gaza," he said.
"On Tuesday, I was scheduled to go for a chemotherapy session in Ramallah, but we were surprised by the closure of Erez crossing.
"My health condition is getting worse, and I am using painkillers to overcome the pain, and my psychological condition is also deteriorating," Ziyad al-Za'noun added.
Israel tightened its blockade of Gaza in 2007 after it was taken over by the Islamist militant group Hamas, citing security concerns.
Hamas does not recognise Israel's right to exist and is designated as a terrorist group by Israel and many other countries.
Gaza's hospitals face severe shortages of medical equipment and medicines largely due to the blockade, but also because of internal Palestinian political divisions.
Many cancer patients need to leave for medical treatment; they have to apply for Israeli permits to exit via the Erez crossing. Most of those who get these are transferred to Augusta Victoria Hospital in occupied East Jerusalem.
More than 90 patients - six of them children with cancer - were due to arrive there in the past week but could not travel, according to Dr Fadi al-Atrash, the hospital's chief executive.
"There is always a need to refer patients primarily to Augusta Victoria and even other hospitals in the West Bank," Dr Fadi said.
"It's because of the lack of services in Gaza, lack of drugs, human resources and appropriate infrastructure."
When the current hostilities end, patients and relatives accompanying them will have to apply for new Israeli permits to leave Gaza.
"When the checkpoints are open, there will be another process for permits. More time will be taken to arrange their exit from Gaza to the hospital and that will add to the delay in their treatment that they have suffered from in the past week," Dr Fadi said.
Already Gaza's power plant is reducing the amount of electricity it generates, to try to save its fuel reserves. If it shuts down, this will have an impact on many different services.
"Preventing the entry of fuel shipments threatens it with a complete stop and will prevent the Gaza Electricity Distribution Company from supplying vital facilities such as hospitals, waste pumps and treatment plants, potable water wells and desalination plants," said Muhammad Thabet, a spokesman for the company.
Normally, some 300 lorryloads of goods enter Gaza each day through the Kerem Shalom commercial crossing with Israel.
In past conflicts, there would have been serious food shortages after several days of closure. However, recently Egypt has eased its tight restrictions on the Palestinian territory, which means food and other goods are continuing to enter.
For now, supermarkets still have stocks of basic items - but many shelves are empty, prompting shoppers to form long queues as they start stockpiling.
Israel's military-run authority that controls entry into Gaza said its crossings had been under the constant threat of rocket fire and remained shut this week.
The Israeli defence ministry said on Saturday that Palestinian Islamic Jihad (PIJ) militants had fired dozens of mortars at Erez and Kerem Shalom since Tuesday.
It also posted what it said was security camera footage showing a blast caused by a mortar fired at Erez.