The latest tunnel was found in Nogales, Sonora, across the border from Nogales, Arizona, according to ArizonaCentral.com.
The discovery comes as President Donald Trump and House Democrats remain deadlocked over funding for a border wall, which has caused a partial government shutdown that is now well into its third week.
On Wednesday, Mexican federal police posted a video on social media showing the tunnel, which measured about 32 feet in length, but they released few other details on the discovery.
The video shows officers opening a manhole in the drainage system under the twin cities of Nogales, where the tunnel was found. It also shows the inside of the tunnel and an officer searching the passage.
Opponents of building more border walls – there are already some 700 miles of wall on parts of the southern border that were in place before Trump took office -- point to tunnels as an example of why border walls really don't work.