The FBI is investigating an underground tunnel in suburban Miami leading to a bank as an attempted robbery by an enterprising would-be thief.

Key points: The tunnel was found beneath the entrance to a bank branch at a shopping centre in Florida

The tunnel was found beneath the entrance to a bank branch at a shopping centre in Florida The tunnel is 60 centimetres to 90cm in diameter and 45 metres in length

The tunnel is 60 centimetres to 90cm in diameter and 45 metres in length The FBI is treating the case as an attempted bank robbery

According to the Miami Herald, the tunnel was discovered after a concerned resident called in what he thought was a pothole in the middle of a busy street in Pembroke Pines, Broward County, to local authorities.

Pembroke Pines Public Works Department crews found an orange extension cord peeking through the hole and immediately called the police.

Police were so alarmed by the find they called in the FBI who found an entrance to the hole covered by a wooden pallet in woods just south of the bank.

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

FBI and police investigate the tunnel which was discovered beneath the entrance to the Flamingo Pines shopping plaza. ( AP: Taimy Alvarez/South Florida Sun-Sentinel )

"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.

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

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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 90cm in diameter and 45 metres in length.

"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 may 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 but they were investigating the tunnel as an attempted bank robbery.