MEXICO CITY, (Reuters) – Police in Mexico found more than 600 Central American migrants in long cargo trucks heading to the United States on Thursday. This was in one of the largest roundups of U.S-bound migrants that Mexican authorities have done in many years.

The video was released by police and showed officers opening the truck’s rear doors and finding migrants wearing heavy coats and hoods.

According to a police statement, almost 200 of 652 migrants discovered in non-descript white refrigerated trucks contained unaccompanied teens and children.

Both U.S. leaders and Mexican officials have been frustrated by waves of Central American migrants and a surge in Haitans trying to enter the United States. They are determined to stem the flow of people fleeing violence, poverty and other natural disasters.

According to a security source, the majority of the migrants in the truck were Guatemalans. They had been taken to a Tamaulipas migrant centre where they would have their legal status reviewed. The source said that Hondurans and Salvadorans were among the migrants being processed. Nicaraguans, Nicaraguans, Hondurans, and one Belizean migrant were also included.

Officials stated that nine of the ten migrants tested positive for COVID-19 on Friday. However, most are only experiencing mild symptoms.

Trucks were stopped on the highway of the northern Gulf state of Tamaulipas. It is approximately 220 miles (335 km) from McAllen Texas. The truck stop was near several grisly migrant deaths in recent years that have been blamed on drug gangs fighting for lucrative smuggling routes to the United States.

Police also arrested four other people, though it wasn’t clear whether they were suspects of being smugglers.