Up to 3,000 migrants, according to organisers' estimates, crossed from Honduras into Guatemala on a trek northward, after a standoff on Monday with police in riot gear.

The Honduran Foreign Ministry called on its citizens not to join the group. The government "urges the Hondurans taking part in this irregular mobilisation not to be used by a movement that is clearly political," it said.

Over the border, Guatemalan police officers detained Bartolo Fuentes, a former Honduran lawmaker, from the middle of the large crowd that he and three other organisers had led from San Pedro Sula, Honduras, since Saturday.

The moves followed comments by US President Donald Trump that indicated his administration would halt aid if the Central American governments did not act, his latest effort to demonstrate his tough stance on immigration.

The Honduran security ministry said Fuentes had been detained because he "did not comply with Guatemalan immigration rules" and would be deported back to Honduras in the coming hours.

Security officials at the Honduran border with Guatemala in Agua Caliente blocked the road to prevent another much smaller group getting through, television images from the border showed.

"We can't attend to people en masse. People are going through one by one," said police spokesman Alex Madrid, in a radio interview.

Guatemala's government said it did not have official figures for how many migrants from the caravan had already crossed the border.

Adult citizens of the countries of Guatemala, Honduras, El Salvador and Nicaragua need only present national identity cards to cross each others' borders. That rule does not apply when they reach Mexico.

Trump took to Twitter on Tuesday to express his annoyance at the caravan, which follows a similar event in May that ultimately led to hundreds of migrants either seeking asylum in the United States or remaining in Mexico.

"The United States has strongly informed the President of Honduras that if the large Caravan of people heading to the US is not stopped and brought back to Honduras, no more money or aid will be given to Honduras, effective immediately!" Trump wrote.

In a later tweet, Trump expanded his threat to include Guatemala and El Salvador.

"We have today informed the countries of Honduras, Guatemala and El Salvador that if they allow their citizens, or others, to journey through their borders and up to the United States, with the intention of entering our country illegally, all payments made to them will STOP (END)!" he said.

US Vice President Mike Pence drove home the point, saying he spoke to Honduran President Juan Orlando Hernandez and Guatemalan President Jimmy Morales warning them to help protect US borders and adding "no more aid if it's not stopped!"

Australian Associated Press