Supt Pearse said formal identification had yet to take place, but Noah’s family had been informed.
“Our thoughts are with Noah’s family and all those who knew him,” he said.
“We have been overwhelmed by the outpouring of public support and people putting on their boots to help.”
Police said at least 1,300 members of the public had helped in the search for the missing boy, who was non-verbal and partially deaf.
People from as far afield as Birmingham and Hampshire had turned up to help.
Searches had widened to include East Bergholt and Manningtree, over the Essex border, on Wednesday.
Divers from the Metropolitan Police were called in to search Decoy Pond, a nearby fishing lake.
The pond is about 350 yds (320m) away from the playground where Noah was last seen.