Photos: Eddie Mitchell
Pictures from Sovereign Harbour in Eastbourne show emergency services at the scene as people were brought ashore, including children being carried wrapped in blankets.
In a tweet, the Emergency Preparedness Resilience & Response Team (EPRR) for East Sussex Healthcare NHS Trust said: "This incident relates to approximately 30 men, women and children arriving at Sovereign Harbour in a small boat.
"No-one has been harmed, although a small number will be brought to our hospitals for a welfare check.
"Sussex Resilience Forum multia-agency partners are in control and managing the situation."
Border Force were in attendance and several people have been detained, Sussex Police said.