GUATEMALA CITY As the first groups from Central America reached the Guatemalan border on Thursday as part of a caravan aiming to reach the United States, regional governments are using coronavirus measures as the latest tool to curtail migration.

Small groups of migrants arrived in the Honduran border town of Corinto on Thursday afternoon, where they were stopped by police demanding negative coronavirus tests, according to local media.

Hundreds more have amassed outside the bus terminal in San Pedro Sula in advance of the caravan's formal departure on Friday morning, according to footage from local television outlets.

Guatemala, Honduras, El Salvador and Mexico issued a joint declaration earlier this week imposing coordinated health measures to deter migration, including requirements to produce negative coronavirus tests at border checkpoints.

The tightening by Mexican and Central American authorities, coupled with pandemic-linked U.S. border restrictions in place since March, represent a sweeping effort to use public health regulations to deter movement along one of the world's busiest migration routes at a time when a fierce second wave of coronavirus is sweeping the region.

In Mexico, the pandemic has killed nearly 137,000 people and the capital's hospitals are spiking with COVID-19 cases.

This week's caravan, slated to depart Honduras on Friday, would be the first of the year and comes six days before U.S. President-elect Joe Biden takes office.

Yet, Central American and Mexican authorities are stepping up efforts to stop migrants well before the U.S. border, which will likely be a relief for Biden, whose aides have privately expressed concerns about the prospect of growing numbers of migrants seeking to enter the United States in the early days of his administration.

On Thursday, Guatemala cited the pandemic in order to declare emergency powers in seven Guatemalan border provinces migrants frequently transit through en route to the Mexican border. The measures limit public demonstrations and allow authorities to disperse any public meeting, group or demonstration by force.

Honduras and Guatemala have announced they will deploy thousands of soldiers to preemptively stop caravan members not complying with health regulations, while Mexico deployed agents to the border with Guatemala.

In online forums, migrants hoping to join the caravan expressed concern on Thursday about the crackdown, with some suggesting searching for "blind points" where they could cross the borders undetected by authorities.

Central America is reeling from economic crises, high rates of violence, and the devastating fallout of two major hurricanes that battered the region in November.

"We barely have food to eat, how do they think we are going to pay for these (coronavirus) tests?" said 29-year-old Ulises Santos from El Salvador, who is hoping to join the caravan.

Migration experts say the public health measures are part of a broader effort by Central American and Mexican authorities, under pressure from Washington, to stop migrants before they reach U.S. territory.

"The U.S. border is moving further and further south," said renowned Honduran human rights activist Ismael Moreno.

"The goal (of local police) is to stop migrants, whether through repression, threats, extortion, or requirements to present a COVID-19 test."

(Reporting by Lizbeth Diaz in Mexico City and Sofia Menchu in Guatemala, additional reporting by Gustavo Palencia in Honduras, Jose Torres in Tapachula, Laura Gottesdiener in Monterrey; editing by Jonathan Oatis and Diane Craft)