The FBI is investigating a tunnel in suburban Miami that it suspects an enterprising would-be thief wanted to use to rob a bank.

The tunnel was discovered after a concerned resident alerted local authorities to what he thought was a pothole in the middle of a busy street in Pembroke Pines, according to the Miami Herald.

Upon investigation, Pembroke Pines Public Works Department crews saw the end of an orange extension cord in the “pothole”. They immediately called the police.

Alarmed police then called in the FBI, whose officers found an entrance to the hole covered by a wooden pallet in bushland just south of the bank.

The tunnel stretched from the nearby wooded area towards the Chase Bank branch in the Flamingo Pines shopping plaza.

“I’ve only seen something like this in the movies – and I’m not even sure I’ve seen this because it’s so small,” Miami FBI spokesman Michael Leverock told the newspaper.

Attempted bank burglary. 50 yard tunnel leads to Chase Bank branch at 390 S. Flamingo Road, Pembroke Pines, FL. Call FBI with information 754.703.2000. pic.twitter.com/nK0rZi8QTO

— FBI Miami (@FBIMiamiFL) January 30, 2019

A generator, winch and wagon were found above ground at the site of the tunnel, suggesting to authorities that rope was being used inside.

Road crews then entered the tunnel and used equipment to tear up the two-lane street leading to the shopping plaza.

The Miami Herald said FBI agents “marvelled” at the size of the tunnel, which was 60 centimetres to 90 centimetres in diameter and 45 metres long.

“You would have to be really small to get in there and it would be very claustrophobic,” Mr Leverock said.

“There’s no way anybody could sit up in there, that’s how small it was.”

Mr Leverock suggested whoever was digging the tunnel might have been working on the dig for months, saying it was not an “overnight job”.

According to the FBI, the bank was not breached and nothing had been stolen. Nonetheless, the tunnel was being investigated as part of an attempted bank robbery.

-ABC