Nearly 200 countries are gathered in South Korea's Busan with the goal of agreeing a deal by the end of the week.

The process caps two years of talks over four previous rounds of negotiations that have been stalled by deep divisions about what the treaty should look like.

Addressing negotiators on the third day of talks, Luis Vayas Valdivieso warned work was not advancing quickly enough.

"The progress has been limited and now time is of the essence," the Ecuadorian diplomat said.

"I must be honest with you progress has been too slow. We need to speed up our work significantly," he added.

"We must accelerate our efforts to reach consensus on the binding instrument by December first."

His call was followed by a string of frustrated speeches from countries including Fiji, Panama, Norway and Colombia.

"While we here sit debating over semantics and procedures, the crisis worsens," warned Juan Carlos Monterrey Gomez, Panama's special representative for climate change.

"We are here because microplastics have been found in the placentas of healthy women," he said.

"We are literally raising a generation that starts its life polluted before taking its first breath."