Young people have been out at "ungodly hours" playing Pokémon Go, Whanganui Police say.
Senior Sergeant Andrew McDonald said police have had "some real issues" around Pokémon Go, but that it has "settled down a little bit now".
Pokémon Go is a smartphone game that has players walk around in real life to catch Pokémon that appear on their phone. The application links to the user's GPS.
Mr McDonald said since the game's release there has been a jump in reports of suspicious activity, including people unlawfully being on a property.
"You basically can't go onto private property without permission of the home owner or the property owner, even if these Pokémon are showing.
"I think the message is that the people playing Pokémon Go avoid going on to private property because they do run the risk of being trespassed or arrested. People have to respect privacy and private property."
Mr McDonald said there had been an issue with young people out "at ungodly hours".
He said children under 18 were out at two or three in the morning when "they just shouldn't be out, really, they should be home in bed".