An incomplete, hand-dug tunnel was discovered stretching from Mexico over the border into Arizona.

U.S. Customs and Border Protection said border agents – with the help of Mexican authorities – found it Tuesday.

They said it was created by drug cartels, originating from a drainage facility in Nogales, Mexico, and extending about 30 feet into Nogales, Ariz. It was about 580 yards west of the Dennis DeConcin Crossing at the Nogales Port of Entry.

LONGEST-EVER BORDER SMUGGLING TUNNEL FOUND STRETCHING BETWEEN TIJUANA AND SAN DIEGO, OFFICIALS SAY

At its deepest point, the tunnel was about 15 to 20 feet down and was left incomplete.

They described the pathway as “rudimentary” with no shoring, ventilation or lighting.

“U.S. authorities will continuously monitor the area until they remediate the tunnel,” CBP said in a press release.

It’s the 126th such tunnel discovered in the Nogales area since 1990, officials said.

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Last month, authorities discovered the longest smuggling tunnel ever found. It went from Tijuana, Mexico, near the Otay Mesa Port of Entry and extended about 4,300 feet into California.

This tunnel featured a complex cart and rail system, forced air ventilation, high-voltage electrical cables and panels, an elevator at its entrance and a complex drainage system, officials said.

The next longest tunnel – at 2,966 feet – was discovered in San Diego in 2014.

Fox News' Morgan Phillips contributed to this report.