Primary pupils and their parents have been kept inside two schools in Worthing after police were told there was a man with a firearm nearby.
Sussex Police said a man raised concerns over someone seen near Victoria Park and Norfolk Street.
"A man showed the weapon to a member of the public. No threats were made and the [member of the public] raised concerns to police," a spokesman said.
After a search the schools allowed children to be collected as normal.
Police said no suspect had been identified, but officers remained in the area.
The two schools involved in the afternoon alert were St Mary's and Heene.