US Secretary of State Rex Tillerson is in Mexico for a meeting with its leader to ease diplomatic tensions over President Donald Trump's trade and immigration policies.

Mr Trump has outraged Mexico by vowing to build a wall along the border to keep out migrants, whom he branded rapists and criminals during his presidential campaign.

He has also threatened to put up barriers to Mexican exports, shift jobs from that country back to the United States and even proposed halting remittances by US-based Mexicans back to their families.

Now he has sent Mr Tillerson to Mexico City to smooth over tensions with the country's government, where he will meet with President Enrique Peña Nieto.

US officials said Mr Tillerson and Mr Peña Nieto would discuss trade and ways to curb migration and drug trafficking.

Mr Tillerson will be joined on the trip by US Homeland Security Secretary John Kelly, who was scheduled to travel on to Mexico from an earlier stop in Guatemala.

"It's significant that the president is sending the secretaries to Mexico so early in the administration. It's symbolic of the meaningful relationship that our two nations have," White House spokesman Sean Spicer told reporters in Washington.

"These are important meetings regarding the president's agenda to improve the quality of lives for both people of Mexico and the United States by combating drug traffickers and finding ways to bolster both our economies through a broader relationship that promotes commerce and legal immigration."

Mr Peña Nieto cancelled a planned meeting with Mr Trump in Washington last month in reaction to the US leader's vow to make Mexico pay for the wall.