But on that day power output did not exceed the peak achieved at the end of April, according to the National Load Dispatch Center.
Hanoi, Da Nang City and Ho Chi Minh City are experiencing highs of 34-37 degrees Celsius these days.
The center forecast that the maximum demand in the north might rise 17% from a record set last year in April-July to 27,481 megawatts.
But production plus imports are expected to only rise by 10% year-on-year to 52.3 kilowatt-hours.
The Ministry of Industry and Trade has been ensuring adequate supply to a region that experienced severe shortages last summer.
A new 500 kilovolt transmission line is being installed to draw power from the central and southern regions.
National utility Vietnam Electricity advises its customers to save power especially during peak hours. It also encourages setting air conditioners at a minimum of 26 degrees.