Trade officials from 12 Pacific rim countries have extended to Friday (local time) negotiations aimed at creating the world's largest free trade zone.
With some of the final differences still not ironed out, a spokesman for the US Trade Representative said a planned press conference on Thursday evening was cancelled and "negotiations will continue tomorrow."
Talks on the Trans-Pacific Partnership (TPP) have been bogged down by several issues, including how the US opens its market to foreign auto parts - particularly from Japanese car makers - and how much Canada is willing to open its market to dairy products like cheese from Australia and New Zealand.
Also still unresolved is the US push to establish lengthier patent protections for biologic drugs, made using living organisms, which is being resisted by a number of the 12 countries involved in the talks - Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam.
There were worries that the negotiators would again not be able to bridge their differences, two months after a meeting of the ministers in Hawaii failed to strike a deal.
Since initiating the talks in 2008, the United States has been hoping to lock in rules on free trade and intellectual property protection that global trade heavyweight China would eventually have to heed.
China, however, has already begun trying to set up its own Asia trade agreement, which analysts worry could take concrete shape if TPP talks fail.