Armed men have violently stormed the southern Brazilian city of Criciúma, mounting an assault on a bank.

Shooting started about midnight local time (03:00 GMT) and lasted more than an hour. Footage posted on social media showed men with guns on the streets.

At about 03:00 local time, Criciúma Mayor Clésio Salvaro said in a tweet that "a major assault" was taking place and urged people to stay at home.

A security guard and a military police officer were injured.

The target of the raid was Banco do Brasil in the centre of Criciúma. The bank has not yet commented on how much money was stolen.

Residents of the city of approximately 200,000 people first reported hearing gunshots at around midnight.

Military police reported that a fire had been set in a tunnel on the main road leading to the city, presumably to prevent the security forces from sending reinforcements to the town. The police headquarters also came under attack.

In other parts of the city, at least six people were used as "human shields" by the armed men, who forced them to sit on a pedestrian crossing to block the road.

Residents posted images on social media of what they described as snipers on rooftops.

Mayor Salvaro told radio station Radio Gaúcha that the "bandits" had made their getaway in a convoy of cars.

Footage posted on social media shows a convoy of black cars leaving the town centre in an orderly fashion.

Assaltantes estão saíndo de Criciúma nesse exato momento pic.twitter.com/GGF8WiqGjv

— Raphael Victor (@RaphaelVictorRV) December 1, 2020

"I have no idea where they're from but they were professionals. Never in the history of this city have we experienced something like this," Mayor Salvaro said of the gang.

It is not clear how much money the attackers made off with but some of their loot was scattered across a city street. Video posted on social media showed residents rushing to gather some of the bills.

December 1: People take money scattered on the floor after a mega robbery in the city of Criciúma - Brazil. Despite the tragedy, Christmas will be better for many people in need. The gang looks specialized and was armed with Bazooka.pic.twitter.com/4UTiavPir7

— Zel Florizel🇧🇷 (@ZellFlorizel) December 1, 2020

Police said four residents were detained after they had scooped up more than 800,000 reais ($150,000; £112,000) from the streets.

So far, there are no reports of any of the bank robbers being detained.