Parties have not reached an agreement on a landmark treaty to curb plastic pollution and more time for negotiations is needed, the talks' chair Luis Vayas Valdivieso told delegates on Sunday.

"We must build on the progress we have made," he said in South Korea's Busan. "There is a general agreement to resume the current session at a later date to conclude our negotiations."

Nearly 200 nations have gathered in the city for negotiations that were supposed to result in a landmark accord after two years of discussions.

"While it is encouraging that portions of the text have been agreed upon, we must also recognize that a few critical issues still prevent us from reaching a comprehensive agreement," Vayas said.

The Ecuadorian diplomat added that "these unresolved issues remain challenging and additional time will be needed to address them effectively".

"While I will not assign a specific percentage to our achievements, it is evident that we have made tangible and meaningful strides in Busan," he said.

A draft text released Sunday afternoon after multiple delays still includes a wide range of options, making clear the ongoing level of disagreement.