Merseyside guns search involves four police forces
Police from four forces across north-west England have been searching areas of Merseyside for firearms.
Officers from Merseyside, Greater Manchester, Lancashire and British Transport Police have been searching parks and fields.
Merseyside Police said the large-scale operation was part of its work to take guns out of the community.
An 18-year-old man was arrested earlier after a shotgun was recovered, a spokeswoman said.
Det Ch Supt Tony Doherty, of Merseyside Police's Matrix team, said: "Today's action is part of our ongoing and unwavering commitment to taking guns off the streets of Merseyside.
"There will be a large number of officers taking part in these searches and I hope it sends out a strong message to those involved in gun crime that we will be relentless in finding your weapons and in finding you."