In the formal negotiations, government delegates convened on Wednesday for intensive talks aimed at securing consensus on key themes.
Currently only about 20% of the draft outcome document here has been agreed.
Preparatory talks had been scheduled to end on Friday this week, but are now set to continue through the weekend and probably up to the point where heads of government arrive for the summit next Wednesday.
Sha Zukang, the chairman of the talks, was optimistic that differences would be resolved in time.
"The determination to work for the common good is encouraging... the whole world is watching us and we cannot afford to let them down," he told reporters.