San Ysidro, California — As the U.S. beefs up security at the border, Mexican cartels are finding new and creative ways to smuggle drugs into the country. A sophisticated tunnel was revealed by U.S. Customs and Border Protection on Wednesday.

It runs three-fourths of a mile and is the longest tunnel ever to be discovered by U.S. officials. It started in Mexico and ran under part of the newly fortified border into the U.S. Deputy Chief Aaron Heitke said smugglers move everything through the tunnels.

"It's going to be people, it's going to be narcotics, the potential for weapons and ammunition," he said.

A look inside a tunnel discovered at the border that starts in Tijuana. U.S. Customs and Border Protection

Ten miles away is another key smuggling route for Mexican drug cartels. Bordering Tijuana, San Ysidro, California, is the busiest port of entry in North America. Sources told CBS News sometimes cartels use spotters to keep track of how the drugs are flowing from Mexico into the U.S.

Drug seizures at U.S. borders are up over the past five years. Cocaine seizures have doubled, meth seizures are up nearly 170% in that same time, and fentanyl seizures are up a staggering 3,500%.

Seized vehicles that CBS News saw have been used to hide drugs in secret compartments. In just one, 24 kilos of meth was hidden in a rocker panel.

"I've seen compartments anywhere we can think of. In floors, in dashes, in gas tanks, in the tires that they're running," Flores said.

The more than 850,000 apprehensions of migrants at the southern border last year, a 12-year high, is also putting pressure on Border Patrol agents.