The negotiation of complicated topics in the updating of the NAFTA will take a number of more rounds of talks, said Mexico's negotiation team head Kenneth Smith.

"There are obviously difficult topics that will not be resolved in this round, that will remain for the following rounds we are going to have," Smith told journalists during the fifth round of North American Free Trade Agreement (NAFTA) talks in Mexico City on Tuesday, Xinhua news agency reported.

These topics include rules of origin in the automotive sector, government purchasing and the US demands for the textile industry, he added.

The chief Mexican negotiator said that the fifth round on Tuesday saw representatives from Canada, Mexico and the US try to move ahead in areas with the smallest differences.

These included e-commerce, best regulatory practices and telecommunications.

He added that all three countries are studying the possibility of holding a "mini-round" of technical analysis in the middle of December.

Concerning the rules of origin for the automotive industry, which Washington wants to raise to 85 per cent, including 50 per cent in the US, Smith said Mexico had still not made a counter-proposal.

"We will not respond with a counter-proposal on rules of origin. We consider that the North American automotive industry is functioning with the rules that exist today, the technical discussion will continue."

Mexico and Canada have stood firm on maintaining these rules of origin at their current level, 62.5 per cent for vehicles and 60 per cent for auto parts.

The three countries are updating the NAFTA since August 16 at the demand of President Donald Trump, who believes the treaty has harmed the American economy and has threatened to scrap it.