This will be in force until 5am on Friday.
Load-shedding will then be lowered to stage 2 until Monday morning.
Mantshantsha said a unit each at Kendal, Duvha, Camden and Kusile power stations tripped overnight.
“Since then, we have returned four units to service. However, these units need to ramp up to full output, which necessitates a high usage of emergency generation reserves today.
“This being the fourth day of extremely high diesel usage, the emergency reserves are being depleted faster than can be replenished,” said Mantshantsha.
He said stage 4 load-shedding would give the power utility the space required to replenish emergency reserves and continue to manage the system safely.
Total breakdowns amount to 15,439MW while planned maintenance is 5,505MW of capacity.
“Eskom would like to apologise for the implementation of load-shedding and will continuously review the situation and act appropriately as circumstances change,” Mantshantsha said.
The power utility appealed to the public to help it limit the impact of load-shedding by reducing the use of electricity and to switch off all non-essential items.