|PM Peter O'Neill has promised to crack down on corruption in Papua New Guinea|
Investigations had shown travel funds had been abused for trips which brought "very little or no benefit", he said.
Any official travelling without his permission could face dismissal.
Mr O'Neill said the government expected to save about K40 million kina (US$19m: £12m) through the travel ban, which was approved by the National Executive Council (NEC) last week and came into effect on 9 January.
He said he and the government had to "stay focused this year, keep our feet on the ground, cut down on unnecessary travels and meetings and conferences that yield little results".
"We have investigated and established that funds budgeted for essential goods and services have been abused to pay for overseas junkets, meetings and conferences that bring very little or no benefit to anyone," he said, adding that productivity was "seriously affected by unnecessary trips".
Officials and government bodies now have to seek the prime minister's personal approval for foreign travel, while permission must also be sought to hold international events within Papua New Guinea.
"Those who breach this NEC decision and directive will face stiff penalties, including suspension or dismissal," the prime minister said.
Mr O'Neill came to power in August last year promising to make the government more transparent and "stamp out corruption wherever it occurs".
Last year, Campaign group Transparency International ranked Papua New Guinea as the 150th most corrupt country in the world, out of 176 surveyed.