(NewsNation) — The death toll of migrants continues to increase as human smuggling attempts have risen in recent years.

The most recent incident happened when at least 48 migrants were discovered inside a tractor-trailer on Monday in San Antonio, Texas, where temperatures swelled to a high of 103 degrees Fahrenheit.

It comes as the record influx has authorities on pace to record more than 2 million encounters this year.

In 2021, U.S. Customs and Border Protection reported more than 550 deaths at the border, most of them were heat-related. That’s more than double the nearly 247 deaths reported in 2020, and the highest since the agency began keeping track in 1998.

The last major incident like Monday’s was in July 2017 when eight immigrants were found dead in a sweltering trailer at a San Antonio Walmart parking lot; two others died later in hospitals.

In May 2003, 19 migrants died inside a tractor-trailer while traveling from South Texas to Houston. Nearly 40 migrants were found at the scene but officials said as many as 200 may have been on the trip.

In May, CBP had nearly 240,000 encounters, a 2% increase from April.