U.S. authorities have discovered a massive haul of cocaine hidden in Dole-brand boxes of bananas that were due to be given to a Texas prison.

The Texas Department of Criminal Justice found the drugs when officers went to pick of the two-pallets of fruit being donated to the prison and noticed someone was off about the weight of them.

The haul is believed to be worth around US$18 million, CNN reports.

"Sometimes, life gives you lemons. Sometimes, it gives you bananas. And sometimes, it gives you something you'd never expect!," posted the department on Facebook.

"One of the sergeants just noticed one of the boxes didn't seem quite right," Jeremy Desel, department spokesperson, told CNN affiliate KTRK. "[He] looked a little further, removed that box off one of the pallets, took a look inside and saw something extraordinarily suspicious."

Within the boxes, officials discovered 540 packages of cocaine hidden among bundles of bananas. The donation came from Port of America in Freeport, Texas, according to the department.

"There are several federal entities that are investigating and it's a pretty significant find for them," Desel was quoted as saying. The DEA and the US Customs and Border Protection are continuing to investigate, the Texas department said.

"Our correctional officers and supervisory correctional officers are trained to notice things out of place that don't seem quite right," Desel was quoted as saying.