Government data released Tuesday show 100,000 more people were caught by federal law enforcement officers while attempting to illegally enter the United States from Mexico in fiscal 2018 than the previous year.
The statistics indicate President Trump's vow to secure the border is proving to be a challenge.
A total of 521,090 people were apprehended between ports of entry as well as denied entry at the ports along the southwest border from Oct. 1, 2017, through Sept. 30, 2018, according to U.S. Customs and Border Protection.
In 2017, that number was 415,517, down from 553,378 in 2016.
[Trump: Democratic obstruction on immigration policy causes 'needless pain and suffering']
Apprehensions in 2017 were at their lowest levels since 1971.
Arrests of people entering without permission has slowly ticked up from around 300,000 in 1970 to between an average of 1 and 1.5 million each year from the mid-1980s through 2006, according to Border Patrol data.
A senior administration official said a major concern in this year's statistics was the number of families and children who made up that annual total.
"We have a border crisis that consists of individuals who are family units and unaccompanied children," an official said during a phone briefing with reports Tuesday afternoon.
Roughly 96 percent of all families were from three countries: El Salvador, Guatemala, and Honduras. Approximately 107,000 families arrived at the border between ports of entry and surrendered to Border Patrol and 50,000 children showed up without a parent.
The official said last month was the highest ever for Border Patrol apprehensions of families in September.
In 2015, fewer than 39,000 families were among those apprehended by Border Patrol -- less than half this year's number. Additionally, the same number of children without parents were reported that year.