A SECRET 1,000ft smuggling tunnel has been discovered under the US-Mexico border by officials who were examining a storm drain.

The sophisticated corridor between Ciudad Juarez in Mexico and El Paso in Texas is kitted out with lighting and ventilation, and reinforced with wooden beams to prevent collapses.

Officials believe it has been used by smuggling gangs to traffic people and contraband into the US.

The entrance was hidden in a storm drain and was discovered on January 10 by US border patrol agents who removed a metal grill covering the hole.

The US agents raised the alarm to their Mexican counterparts, and investigators are looking into whether local officials knew of the tunnel’s existence.

General Jose Lemus, commander of Ciudad Juarez’s military garrison, said the tunnel is six feet high and four feet wide, making it large enough to comfortably walk through.

He added that it “must have taken a long time” to build, suggesting “it could have been one or two years”.

Victor Manjarrez, a former US Border Patrol sector chief with over 20 years of experience, said the tunnel was likely built by traffickers.

According to him, connecting a tunnel through a storm sewer system is a common tactic among these criminals.

He said: “It’s actually the most common way.

“Most of the tunnels, that’s over, I want to say it’s about 230, 240 tunnels along the southwest border since ’91.

“Most of those attach to some kind of infrastructure in the US.”

An investigation has been opened to find out who built and used the tunnel, and who knew about it.

Victor said: “This is definitely not a mom-and-pop operation at all.

“It’s gone way beyond that.”

Jose said that the Mexican Attorney General’s Office is responsible for the investigation and will be in charge of determining if authorities were complicit in its construction.

Anthony Scott Goof, El Paso Chief Patrol Agent, said: “We are proud of the Agents who discovered this smuggling infrastructure used by transnational criminal organizations.

He added: “Our Agents are relentless in searching and surveying every square mile of the El Paso Sector.”

Officials have vowed to seal the tunnel off so it can never be used again, and workers have already been pictured blocking it with concrete on it on the US side.

Border security is being ramped up on both sides as President Trump takes office today.

He has promised a much tougher approach to immigration, including mass deportations “very early, very quickly” in his presidency.

He told NBC: “We’re already geared up, and it will begin.

“We have to get the criminals that have come here illegally out of our country.”

He reaffirmed his immigration pledges to a Washington rally the day before his inauguration on Sunday.

He said: “These are rough people [coming over the border] and they’re getting the hell out of our country – they’re out.”

“The border security measures I will outline in my inaugural address tomorrow will be the most aggressive, sweeping effort to restore our borders that the world has ever seen.”

NBC News also reported Immigration and Customs Enforcement officials are planning several raids in Chicago, Illinois, after Trump gains power.

A source told the broadcaster that multiple locations would be targeted, and these could start as early as Tuesday.