Mandurah police allegedly uncovered weapons and drugs when they caught a man riding a stolen motorcycle in the early hours of this morning.
Police say a 26-year-old Halls Head man was riding a stolen motorcycle along Tankerton Way in Coodanup at about 12.45am.
The man failed to stop and fell from the bike as he attempted to flee.
Police arrested the man and discovered several illegal items in his backpack.
A loaded semi-automatic pistol, a firearm disguised as a knuckleduster, knives, a significant amount of cash, drugs believed to be methylamphetamine and drug paraphernalia were among the alleged items.
The man was treated for minor injuries at Peel Health Campus and was taken into police custody.