A Southern Water spokesman said: “We are aware of the ongoing multi-agency emergency response at Testwood Lakes following reports of a missing young person.
“Our thoughts are with the boy’s family and friends at this deeply worrying time.
“We would strongly urge members of the public to follow police advice, avoid the area, and allow emergency services to carry out their search.”
BBC reporter Hannah Walsh, speaking from the scene earlier, said: “The road into Testwood Lakes is closed, with a police closure sign and cones in place.
“A number of cars have pulled up to collect people – possibly at the lakes before it was evacuated – and many of them have been sat opposite the lake entrance on a grass area in the shade, trying to stay cool.”
She added that although the first wave of emergency service vehicles had left, two search and rescue units had now arrived.
