Around 40 people have been detained and are being processed at Hill Head Sailing Club by immigration officers, and the Gangmasters and Labour Abuse Authority.
Hampshire police confirmed there were more than 40 cockle pickers in the area but they did not speak with them all.
In a joint statement, Hampshire police said: ‘As part of an investigation to target modern slavery, the Gangmasters and Labour Abuse Authority (GLAA) are speaking to potential victims on the seafront in Hill Head today following multiple reports of shellfish gathering.
Woman, 44, whose large Dobermann dog mauled girl, 3, on Leigh Park street released back into neighbourhood by police
WATCH: This is the moment a man with a grudge fire-bombed a family's garden in Leigh Park
Plans for redevelopment of Knight and Lee in Southsea get the green light - and work will begin soon, vows developer That Group
'It was just sheer panic from everyone': 'Horrific' bedroom fire in Paulsgrove ripped across several house roofs with 'pouring' smoke being seen from the motorway
Unidentified woman’s body found in water as Hampshire police investigate ‘unexplained’ death
'The investigation is being led by the GLAA and supported by Hampshire Constabulary, Fareham Borough Council, and Immigration.
‘We received information regarding large-scale cockle picking along the shoreline, and the investigation will focus on the suspected exploitation of the workers collecting the shellfish, contrary to the Gangmasters (Licensing) Act 2004.
‘On arrival, officers found a large group of people collecting shellfish on the shore.
‘Around 40 people are currently being spoken to as potential victims of labour exploitation at two separate locations on the shoreline.
‘Officers from Hampshire Constabulary’s special constabulary, marine unit, the drone unit and the roads policing unit were involved in today’s operation, alongside partners.
‘We would like to thank Hill Head Sailing Club for their co-operation as we make enquiries in the area.
‘Thousands of people from across the world are being exploited in conditions of slavery here in the UK.‘If you suspect someone to be a victim of modern slavery or human trafficking, contact the 24/7 Modern Slavery Helpline on 0800 0121 700, or 999 for emergencies.‘You can also call the GLAA on 0800 432 0804 or alternatively call Crimestoppers on 0800 555 111 or visit gla.gov.uk’