According to the latest Public Health England (PHE) figures a total of 28 cases of the Delta variant, which originated in India, were recorded by June 9 in the city.
Between one and four cases were recorded by June 2.
In Havant 15 cases of the Delta variant were recorded by June 9, with seven in Gosport, 18 in Fareham and 21 in East Hampshire.
Health Secretary Matt Hancock said the Covid-19 mutation now makes up 91 per cent of new cases in the UK, with evidence suggesting it may be more dangerous than the Alpha – formerly known as the Kent – variation.
The cases in Portsmtouth were among at least 3,719 cases of the variant identified across the south east – the third-worst affected of England's nine regions.
Dr Jenny Harries, chief executive of the UK Health Security Agency, said: ‘With numbers of Delta variant cases on the rise across the country, vaccination is our best defence.
‘If you are eligible, we urge you to come forward and be vaccinated.
‘Remember that two doses provide significantly more protection than a single dose.
‘However, while vaccination reduces the risk of severe disease, it does not eliminate it.
‘With data showing that Delta is significantly more transmissible than Alpha, it is just as important as ever to follow public health advice, which has not changed.
‘Get vaccinated, work from home where you can and remember ‘hands, face, space, fresh air’ at all times. These measures work, and they save lives.’
The north west – where variant hotspots Bolton and Blackburn are located – continued to have the highest numbers identified – 16,825 Delta variant cases have been recorded there.
PHE said on June 11 that 42,323 cases of the Delta variant have been confirmed in the UK, up from 29,892 a week ago.
The increase in confirmed cases has been driven partly by a reduction in test turnaround times and a faster process for identifying cases of the variant, PHE said.
Growth rates for Delta cases are high across all parts of the country, it added, with cases doubling every 4.5 days in certain areas.
Different PHE figures show that 42 people across England had died with the Delta variant as of June 7.
Of them, 23 were unvaccinated, seven had received their first dose more than 21 days prior and 12 died more than two weeks after receiving their second jab.
The figures also show that two thirds of the 1,234 people who attended A&E in England between February 1 and June 7 and who were confirmed as having the Delta variant of coronavirus were unvaccinated.