Authorities spotted the men carrying bags and walking up the bank of the Mekong River.
When ordered to identify themselves, the gunmen opened fire, Pol Maj Gen Chaiyaporn said.
All of the drug smugglers and their armed guards escaped but left behind the 200kg of cannabis.
In Chiang Rai, provincial governor Pongsak Wangsamoe told a press conference yesterday that a special task force on drug suppression had seized 450,000 tablets of methamphetamine and a motorcycle.