A pleasure boat allegedly sailing near Bournemouth beach on Wednesday has reportedly been impounded by police after the deaths of two young people who got into difficulties in the sea. The Dorset Belle, a cruise boat that operates from Bournemouth pier, was under guard in Poole harbour, the Times reported, quoting a police source as saying: “This vessel is under a police cordon. No one is permitted onboard or to touch the vessel.” Police investigating the circumstances that led to the deaths of a 12-year-old girl from Buckinghamshire and a 17-year-old boy from Southampton on Wednesday have said early investigations indicate there was no physical contact between any vessels and the swimmers. A man in his 40s who police said was “on the water at the time” has been arrested on suspicion of manslaughter. He was released on Thursday evening under investigation. On the day of the deaths, the Dorset Belle, which can accommodate 80 people, made numerous circuits of Bournemouth pier, according to the online tracker Marine Traffic, suggesting it was in the vicinity of the incident several times, the newspaper said. RNLI lifeguards rushed into the sea to get to the swimmers during the incident, which happened off a crowded beach at 4.30pm. Dorset police said they received a report from paramedics at 4.32pm of people requiring assistance. Emergency services attended and 10 people were recovered from the water. The 12-year-old and 17-year-old had sustained “critical injuries” and later died in hospital. The eight others were treated at the scene by the ambulance service for injuries that were not life-threatening. An investigation has been launched by Dorset police, working alongside the Marine Accident Investigation Branch and the Maritime and Coastguard Agency. Rachel Farrell, assistant chief constable of Dorset police, said on Thursday that there was no suggestion of people jumping from the pier, or of jetskis being involved. Reading from a statement, she said: “To avoid further speculation, I am able to tell you that it is clear that yesterday a number of people already in the water got into difficulty and we are investigating the circumstances or event that caused that to happen. “Early investigation indicates that there was no physical contact between a vessel and any of the swimmers at the time of the incident. “I can also confirm there is no suggestion of people jumping from the pier or jetskis being involved.” She said as a person was in custody she could give only limited information about the “complex” investigation at this stage. The two young people who died were not related, and came from different parts of the country, she said. The early indications were that the incident involved “different people from different families who weren’t known to each other and who were enjoying the water”. She added: “I would sincerely like to thank members of the public who helped people in trouble in the water. I am also very grateful to the wider beachgoers who really quickly moved from the beach and allowed emergency services to do their work.” The emergency services “provided a really swift and coordinated response”, she said. She asked people not to speculate about the circumstances surrounding the incident and to refrain from circulating videos on social media. Urging anyone who saw what happened, or had any information that may assist, to come forward, she said people could upload any relevant phone footage to the major incident team, codenamed Operation Marble. Local unconfirmed reports said an announcement had been made warning bathers of a dangerous riptide. Nicola Holton, 43, who had been on the beach with her husband and their two children, said: “When we first spotted the swimmers in distress they were far out to the east side of the pier. “A lifeguard ran into the water with a surfboard and it seemed to take ages for him to get to them. There was an announcement to get out of the water and then the lifeguards started bringing people back to shore. “A few were taken to the lifeguard tent and then we saw the young man and the girl being brought out. We were packing up our things to leave as quickly as we could. It was just awful.” Tom Saunders, a surfer, told Sky News: “I was surfing on the west side with about four other people and we heard the lifeguard sirens going off, making announcements, and the beach got cleared either side. “Obviously we knew something had gone on and the helicopter was coming so we knew it was serious. “Unfortunately, I saw someone receiving CPR. The lifeguards put up a screen so no one could see, but unfortunately from where we were we could. “The [lifeguard] jetskis were going round the pier looking for stuff, so me and three other surfers offered to help and actually paddled into the pier to have a look. “They said there were two people missing at the time, then after about half an hour they said everyone was accounted for and we just carried on.” Conor Burns, the MP for Bournemouth West, said the incident was a “salutary lesson” that “danger is ever present” on beaches and the ocean. “Thoughts with everyone associated with the dreadful events unfolding in Bournemouth this evening,” he said. “A salutary lesson that our beaches and ocean can give much pleasure but danger is ever present. Thanks to the lifeguards and the air ambulance, who we can take for granted.”