At least 23 vehicles were parked on land next to the Blue Reef Aquarium between Clarence Esplanade and Serpentine Road this morning.
The green space is surrounded by boulders to restrict vehicle access, but it is believed one of the rocks was moved.
One man staying on Southsea Common, who asked to remain anonymous, said the group would seek to stay put for ‘three or four days’.
Portsmouth City Council leader Gerald Vernon-Jackson said the travellers arrived after a ‘gap appeared in the defences’.
He said: ‘We will be going to court to get them evicted as soon as we can.
‘We will do everything we can to get the land back to normal as quickly as possible.’
Speaking to The News at the site, one traveller said: ‘If there were more sites available then we wouldn’t be here. There’s a shortage.’
The settlement comes after at least nine unauthorised camps were pitched up across the Portsmouth area last year.
Southsea Common was among these, with travellers also going to Canoe Lake, Watersedge Park, Ferry Road in Eastney, Five Heads Recreation Ground in Horndean and others.
In following procedure, Portsmouth City Council must do the following to evict travellers from its land:
- Show they are on the given land without consent
- Make enquiries regarding general health, welfare and children’s education
- Ensure the Human Rights Act 1998 is fully complied with