Airlines operating in Papua New Guinea have been urged to tighten security after police found a rocket launcher and grenades concealed in a passenger's luggage.

Radio Australia's Firmin Nanol reports that police in PNG's Western Highlands province found a rocket launcher and nine grenades in the traveller's baggage at Mt Hagen airport last week.

Commander Thomas Eluh says a man transported the ammunitions into the province in a light aircraft from Kikori, in PNG's Gulf province.

He says they could have been destined for use in tribal fights in PNG's Highlands.

One man has been arrested and is in police custody as investigations continue.

Another live hand grenade has reportedly been found under a seat on PNG's national airline, Air Niugini.

The airline says it has tightened security and plans to place air marshalls on all domestic flights.

SOURCE: Radio Australia