At least 32 firefighters were called to Handsworth House, in Quinton Close, Somers Town, after unattended cooking caused smoke, setting off the smoke alarm.
It happened at 12.45am and saw eight fire appliances from across the area attend the 17-storey block.
Following the disaster at Grenfell Tower in London the fixed response to high-rise incidents in Portsmouth has increased from five appliances to eight.
Crew manager Simon Lovelock, from Southsea station, said: 'Two people in the flat were escorted to safety.
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'Other people did come out but that was of their own accord, we didn't evacuate them.
'By the time we'd arrived it was done, and it was just a pan of black.
'We removed that and turned the hob off and put two of our positive pressure ventilation fans to clear that.'
Residents of other flats were not evacuated.
Crews attended for around 90 minutes.
Earlier in the evening at 9pm crews were called to a bungalow in Waterloo Street, Portsmouth, where a woman suffered burns to her arm.
She had put out a pan fire using an extinguisher but hurt herself in the process.
'We gave her immediate medical care and made sure her burns didn't get any worse,' Mr Lovelock said.
Two crews from Southsea attended for around 90 minutes.
Medics from the ambulance service attended.