Army bomb disposal experts were called to student halls of residence in Leeds yesterday after a tip-off prompted police to carry out a search.
West Yorkshire Police said officers initially attended the Kirkstall Brewery halls of residence in Broad Lane at 2pm.
They were acting on information received about possible firearms at the site, which provides accommodation for up to 800 Leeds Beckett University students.
A police spokesman said: "A number of items were found in a flat including what appeared to be a grenade-type device. The premises were evacuated while Army specialists attended. They confirmed it was an imitation.
"Two other imitation firearms were recovered and were confirmed as deactivated weapons that presented no danger."
Police said a 19-year-old man was later arrested by officers at an address in Scunthorpe.
He is still being held in custody today as enquiries continue.
Meanwhile, the local neighbourhood policing team has been working with Leeds Beckett University staff to reassure students that there is no ongoing risk.
A number of people posted messages on social media yesterday about having been evacuated from their flats or seeing the police response.
Cal said on Twitter: "There’s only Kirkstall that could have the bomb disposal unit turn up and start searching rooms for five hours."
Harrison Boase said: "There's apparently a bomb threat at Kirkstall Brewery uni accommodation. CSI and bomb disposal are here."
Amelia said: "There’s like two unmarked police car, police car a bomb disposal team and soldiers and one of the houses have been evacuated."
Connor Marson said: "Love it getting kicked out of our flat, then bomb disposal and CSI turn up. Would seriously recommend kirkstall like."