Police Commissioner Fuiavailili Egon Keil had already implemented three since he became Commissioner in 2015.
Past amnesties allowed owners of unlicensed firearms and illegal ammunition and explosives to turn them in without risk of prosecution.
However illegal firearms continued to be a problem, seemingly alongside the growing illegal drugs trade.
The Samoa Observer newspaper reported a recent police raid on a home not far from Apia netted at least seven pistols and nine rifles.
