In a statement last night, police confirmed the location of the attack where they had identified a "male suspect".
But the officer in charge was not available to comment further.
"There were a large number of people present at the beach at this time and police are asking for the assistance of members of the public who were in this area to please contact them," the statement said.
Oreti Surf Life Saving Club secretary Sally Wilson was shocked to hear about the attack.
"It's very popular with families, it's a very family oriented beach. That's just disgusting, it's absolutely terrible."
Mrs Wilson said usually there were no problems at the beach.
"We just don't have any major dramas.
"You get the odd one that does the odd skid up the beach, but we don't normally have any problems at all. It's just a nice safe beach."
Invercargill and Oreti residents were outraged by the attack and posted comments about what had happened on social media sites.
Locals said they were shocked and appalled that the 8-year-old had been subjected to such an awful ordeal.
Oreti Beach is 10km west of Invercargill, and was a key location in the film, The World's Fastest Indian - about the life of Invercargill-born motorcycle pioneer Burt Munro.
Oreti became famous when Anthony Hopkins, playing the role of Munro, raced his motorcycle along the beach.
