Chinese nationals represent the fifth-largest population of illegal immigrants in the U.S. but not all of them are undocumented because they overstayed a visa. Many are arriving in the U.S. illegally via the southwest border.

The phenomenon is on the rise, in particular, in the San Diego sector where the number of Chinese migrants apprehended entering the U.S. illegally has increased over 1,200 percent just in the first eight months of fiscal year 2016, according to Customs and Border Patrol data obtained by the San Diego Union-Tribune.

The San Diego Union-Tribune reports that Border Patrol agents in the San Diego sector apprehended 663 Chinese nationals from October to May, compared to just 48 Chinese nationals last fiscal year, five in fiscal 2014, and eight in fiscal 2013.

Prior to 2013, Border Patrol spokeswoman Wendi Lee told the paper, the sector did not see Chinese nationals coming to the U.S. through the southwest border.

When Border Patrol apprehends border crossers from countries other than Mexico, depending on the circumstance, they are often turned over to Immigration and Customs Enforcement, which considers whether or not to hold the migrant while they await immigration hearings.

Lee told the Union-Tribune that smugglers are able to squeeze the Chinese nationals seeking entry for tens of thousands of dollars.

“We’re talking anywhere from $50,000 to $70,000 per person,” Lee told the Union-Tribune. “The further you travel from, the more arrangements these criminal organizations have to make, the more expensive it will get.”

The increase in San Diego comes amid an overall increase in migration to the U.S. from Asia.

According to the Pew Research Center, since 2011 Asia has been the largest region of origin for recently arrived immigrants. Pew estimates that by 2055 Asian immigrants will comprise the largest immigrant group in the U.S.