Antonio Guterres called upon the nations' governments to make climate change a priority.
The World Economic Forum brought various concerns on the global economy.
The charity body says billionaires around the world saw their combined fortunes grow by US$2.5 billion each day in 2018.
At least 97 activists are behind bars in Vietnam as of April this year, with some 40 convicted this year on various anti-state charges.
Vietnam's Prime Minister Nguyen Xuan Phuc told the forum technology could spell doom for the Asian factory model of growth that has driven his country in recent years.
Despite sweeping economic reform and increasing openness to social change, Vietnam's ruling Communist Party retains tight media censorship and does not tolerate criticism.
Debbie Stothard was refused entry to Vietnam to attend the WEF-Asean summit.
Government should introduce a Report Card on Competitiveness, to keep track of our efforts to make improvements, in comparison to other countries.