"It's something you see in the movies ... They dug a 200m [650ft] tunnel that goes underneath two [city] blocks. They've been digging for three months," a police investigator, Francisco Queiroga, said. The tunnel went four metres below the vault.
The thieves broke into a branch of the Central Bank in Fortaleza, in the state of Ceara, 1,500 miles north-east of Sao Paulo, over the weekend and removed 156 million reals.
The 500sq metre vault is surrounded by 2m-thick reinforced concrete walls. The theft was not discovered until yesterday.
"The tunnel was dug right underneath the vault," Mr Queiroga said. "We've never heard of so much money being stolen from a bank in Brazil."
Federal police in Ceara said between six and 10 people were suspected of doing being involved.
The theft exceeds the amount stolen by Britain's "Great Train Robber" Ronnie Biggs, who fled to Brazil and lived in the country for many years.
He and 11 other gang members robbed a Glasgow-to-London mail train in 1963 and made off with £2.6m - some £30m in today's money.Reuse content