"We have nearly 1,600 students, and guests have also confirmed their participation, so we cannot cancel the ceremony," Nguyen Le Quoc Dung, vice principal of Phu Hoa 3 Elementary School in Thu Dau Mot city said.
"With this power cut notice, we have to cancel some activities."
Besides, the school would have to hire a generator, he added.
A seafood restaurant in the city said it could only open in the evening on May 26.
"The power cut is from 6am to 6pm, and so we cannot open with the hot weather and without fans and air conditioners. We also had to cancel pre-orders for that day."
Many factories have had to change their schedules or suspend operations due to load shedding since last week.
A construction materials manufacturer in HCMC has had to stop production at its facilities for one to five hours on some days last week.
There is no schedule for this week yet, but its CEO said that if the power outages continue, production would badly hit.
Pham Xuan Hong, chairman of the HCMC Textile and Garment - Embroidery Association, said businesses are on edge over the power cut.
"Electricity is critical to production."
In Hanoi, some districts are having outages for four to six hours from May 23 to 25.
Power has been cut for two days from 3:30am to 11am on May 23 and 24 in some places like in Giap Bat Ward in Hoang Mai District.
In the south, cuts are scheduled in many provinces from May 22 to 29.
Some like Binh Duong and Dong Nai will even have six to 12 hours of load-shedding.
Power companies blamed the shortages and load-shedding on record demand though there have also been technical problems and maintenance work.
Vo Quang Lam, deputy director of Vietnam Electricity (EVN), said the recent heat has reduced the efficiency of thermal power plants and their output.
Water levels in many large hydroelectric reservoirs are at their lowest in years, he said.
As of May 21 there was only enough to generate 2.9 billion kWh, nearly 1.73 billion kWh lower than expected.
Meanwhile, power demand has shot up due to the prolonged heat, and is expected to increase even more, he said.
Bui Trung Kien, deputy director of EVN HCMC, said defects in the power grid have been identified and fixed in the past few days, and the city would have enough power to fully meet demand by the end of this month.
EVN said the Hanoi outages are only for repair and maintenance of the grid to ensure smooth delivery of electricity.
Lam said EVN has negotiated with Vietnam Oil and Gas Group (Petrovietnam) and Vietnam National Coal-Mineral Corporation (Vinacomin) to increase supply of gas and coal.
Nevertheless, households and businesses are encouraged to conserve electricity, he added.