WASHINGTON (AP) — Border Patrol agents stationed in South Texas are the busiest in the country, arresting tens of thousands of children illegally crossing the border without their parents and thousands more families with children.

Here's a look at some numbers on the immigration situation.

—In the last budget year, Border Patrol agents arrested about 420,000 people, most of them along the Mexican border. That followed a three-year trend of near record low numbers of apprehensions.

—Overall, the number of immigrants caught sneaking across the border remains at near historic low levels.

—The last time so few people were arrested at the country's borders was 1973, when the Border Patrol recorded just fewer than 500,000 arrests.

—The number of people being arrested at the border remains dramatically lower than the all-time high of more than 1.6 million people in 2000.

What makes the situation on the border today different is who is crossing and where.

—Since 2012 the number of unaccompanied children caught at the border has been steadily rising.

—Compared to the first 10 months of the 2013 budget year, the number has more than doubled. And since most of the children are from Central America, they can't be quickly sent home like their Mexican counterparts.

Compounding the problem is the arrival of more than 55,000 people traveling as families, mostly mothers with their children. Like the child immigrants, the majority of the families are from Central America. And with room to detain fewer than 1,000 adults with children, many of the families have been released with orders to report back to immigration officials after getting to their final destinations inside the United States.

The situation has been described as an "urgent humanitarian crisis" by President Barack Obama and prompted the president to ask Congress to approve an emergency $3.7 spending bill.

Most of the border crossers are being caught along a narrow stretch of border in the Rio Grande Valley in Texas, taxing resources in a single corner of the border.