Demonstrators assembled near Haslar Marina in Gosport on Sunday amid reports that authorities were preparing for the arrival of a boat carrying 149 migrants.
The dinghy was shadowed by French rescue vessels until it was met by two RNLI boats in English waters.
Around 350 people gathered during the incident, with the crowd dispersing by 2am.
Hampshire and Isle of Wight Constabulary has since confirmed it arrested 12 people on suspicion of a number of offences, including the assault of a police officer, criminal damage, and being drunk and disorderly.
A small number of officers were treated at the scene for injuries, and another person was treated for chest pains by the south central
The migrants onboard will now be taken to Kent to undergo processing, the Home Office confirmed.
Hampshire and Isle of Wight Constabulary earlier said it deployed officers to Gosport to “support our partners in the event of an emergency at sea”, with ambulances and coaches spotted in the area.
The protest was mostly peaceful, but there were reports of flares being set off and scuffles with the police.
Officers prohibited the use of face coverings to “conceal identity during any protest activity”.
They also directed protesters to a designated area inside a car park and warned that failure to comply “is a criminal offence and may result in arrest”.
A government spokesperson said: “The Border Security Command works around the clock to protect our border. We have established contingency plans to make sure we can securely disembark, check and process all small boat arrivals.
“Migrants will be transported to short term holding facilities in Kent where they will be processed as normal and undergo stringent health, security and biometric checks.”
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Last month, protesters gathered in the area after reports suggested that migrants would be arriving on a dinghy – but they were instead taken to Dover by sea.
The vessel, carrying 51 migrants, spent around 30 hours at sea after departing from Normandy.
The migrants eventually arrived in Dover after being transferred to Border Security Command boats.
It is estimated that 19,451 Channel crossings have taken place this year, a 43% decrease on this time last year and a 23% drop from this stage in 2024.
