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Immigration authorities said they have seen a “dramatic increase” in the number of large groups of 100 or more migrants being apprehended at the U.S. southern border over the last few months.

Since the start of October, smugglers brought 53 large groups of migrants to the border in the areas of El Paso and the Rio Grande Valley in Texas, and Tucson and Yuma in Arizona, U.S. Customs and Border Patrol said in a statement. All of the 8,797 migrants in those groups were apprehended.

The vast majority, 84.6 percent, were migrant families. Another 11.5 percent were unaccompanied children, CBP said. More than 99 percent were from the Northern Triangle countries of Guatemala, Honduras and El Salvador.

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Crossings at the southern border are significantly lower than they were from the 1980s through the 2000s. Since the year 2000, apprehensions have fallen from yearly highs of up to 1 million or more migrants, according to CBP data.

Still, CBP says the number of migrant families apprehended along the border with Mexico in recent months surged by 280 percent since the same time last fiscal year.

December set a record for the number of migrant family members taken into custody, with 27,518 apprehended during the month between official ports of entry into the U.S., according to CBP.

From October through December, 75,794 family members were apprehended, according to the Department of Homeland Security.

In the prior fiscal year that ended in September, 396,579 migrants were apprehended in between ports of entry.

CBP also said it has seen an increase in the number of migrants needing medical attention. Border Patrol transported 2,224 people to local hospitals since Dec. 22 of last year, comprising about 5.3 percent of all southwest border arrests, according to CBP.

On Jan. 15, Border Patrol arrested a group of 247 migrants, with 50 people requiring "immediate treatment/evaluation from a medical professional at a hospital," CBP said. That group was apprehended in New Mexico.

Earlier this month, CBP released video showing what it called the largest single group of asylum seekers ever crossing into the U.S. The group of 376 Central American migrants, 179 of them children, were seen on the video both going over and burrowing under a border fence near San Luis, Arizona. All of the migrants voluntarily turned themselves into CBP after crossing into the U.S., according to the agency.