All the countries involved in the six-way dialogue to end North Korea's nuclear programme were in Hanoi except for the North Koreans themselves.
Pyongyang has agreed to return to the negotiating table after a year-long gap but no date has been set.
The 21 leaders of the Asia Pacific Economic Co-operation (Apec) forum issued a Hanoi Declaration after their summit outlining steps to liberalise commerce in a region that accounts for nearly half of global trade and pledging to "combat terrorism in every form and manifestation".
In it, they pledged to study the feasibility of a free trade zone comprising 21 major economies which would stretch from China to Chile and account for 60 per cent of global economic output.
"We instructed officials to undertake further studies on ways and means to promote regional economic integration, including a Free Trade Area of the Asia Pacific as a long-term prospect," the statement said.
While there are "practical difficulties" in negotiating the so-called FTAAP, it would be timely to "seriously consider more effective avenues" towards liberalising trade and investment, they noted.
Results of the studies will be reported back to them at the Apec forum in Australia next year.
On the first day of the summit on Saturday, they pledged to make compromises on farm subsidies and industrial tariffs in an "urgent effort" to jump-start the Doha Round of trade talks.
The Hanoi Declaration acknowledged the need to take action to "protect legitimate financial and commercial systems from abuse".
This appeared to be a veiled reference to the kind of financial curbs the US has taken against North Korea over alleged illicit activities such as counterfeiting.
Leaders wore traditional Vietnamese
tunics for the annual family photo
But a section highlighting terrorist threats to rail and mass transit systems in the region and Apec's opposition to trafficking in weapons of mass destruction was deleted in the final text.
No explanation was given, but some Apec members have expressed reservations that a group founded in 1989 to deal with trade and economic issues has been veering too hard in recent years towards security problems such as North Korea.
The leaders held their summit at a new $270 million convention centre on the outskirts of the capital before donning traditional Vietnamese ao dai tunics of blue, green, pink, orange and yellow silk for the annual family photo.
The final declaration also called for increased co-operation on to battle bird flu and other pandemics, improve disaster planning and ways to rescue trade in the event of major disruption caused by a terrorist attack or other calamities - all issues of immediate concern to many countries in the region.