CLAY COUNTY, Fla. -

Five Cuban nationals have been arrested in connection with an extensive marijuana grow operation in four foreclosed homes in Clay County, according to the Sheriff's Office.

Deputies said the operation included, among other things, the construction of buried, underground grow rooms behind and under one home in the 2900 block of Guava Court in Middleburg.

Arrested were Jaime Mora, Antonio Santos, Yandriel Gonzalez, Jonny Gordillo Valdespino and Raluxi Erbiti.

Investigators in Clay County said they've never seen a grow operation this sophisticated.

PHOTOS:Underground marijuana grow operation

According to the Sheriff's Office, the drug dealing suspects buried two 40-foot semi-trailer beds 20 feet deep to create an underground grow house.

"It was accessed by a false trap door that went down into the cargo container," Sheriff Rick Beseler said. "Deputies, when they raided this, had self-contained breathing apparatus because of the danger of the fumes in the bunker."

The grow houses were equipped with air conditioning, lights and temperature monitoring devices, deputies said. They said the dealers scaled JEA power poles and stole power to run the underground operations. They converted the power off live power lines from 15,000 volts to 110 volts, running a conduit underground to power the grow operation.

"There for a while, if you walk out, it was so powerful," said Ashley Crater, who lives next to one of the grow houses. "I would get headaches and lightheaded. I didn't know what was going on."

Marijuana was not being sold in Clay County but shipped to South Florida, investigators said. They said all material was purchased out of the state.

Deputies said the drug dealing suspects claimed to be construction workers. Investigators said the men are legally in the United States but are not citizens.

Deputies said the investigation was underway for two months after a Florida Highway Patrol trooper conducted a traffic stop. They said the operation has been in effect for three to four years.

The Sheriff's Office and federal drug agents conducted simultaneous drug raids.

The drugs seized in the grow operations were valued at about $864,000. Investigators said it was a high-grade marijuana valued at about $4,000 to $5,000 a pound.