Unrest and violence erupted in the center of Chicago early on Monday after weeks of bubbling tension in a number of neighborhoods across the city and protests on Sunday after a man was shot by police on the south side.

In the violence, a security guard and a civilian were struck by gunfire and taken to the hospital in critical conditions.

A total of 13 police officers were also injured, including a sergeant who was struck by a bottle while another had his nose broken.

During a press briefing, Chicago Police Superintendent David Brown said the looting was related to a shooting in Englewood on Sunday afternoon, when police officers responded to a report of a 20-year-old man with a gun.

At one point early on Monday, shots were fired at police and officers returned fire.

Brown further added that a heavy police presence was expected in the downtown area until further notice.

The first looting incident took place in South Chicago, Brown said, but “soon, car caravans were headed into the Loop” to begin looting.

It is “pure criminality”, he said.

Hundreds of people were seen damaging storefronts and stealing goods on Sunday night. Several people were videoed taking merchandise from stores including Walgreens and CVS, with some bringing the goods to waiting cars.

Chicago Mayor Lori Light foot called the act a “felony criminal conduct” and “an assault on our city”.

She called on the public to help apprehend the looters.

For several hours on Monday morning, the bus and train service was suspended in downtown Chicago, and all downtown bridges except one were raised, according to a Chicago Transit Authority (CTA) announcement.

CTA restored normal service shortly before 8 a.m., but the major streets throughout downtown Chicago remain closed.

Taking to Twitter, the Chicago Transit Authority said that the train and bus service into downtown was temporarily suspended at the request of public safety officials.

The partial shutdown of Chicago echoes similar moves taken in the wake of the death of George Floyd, a black man who was killed by police in Minneapolis on 25 May.

Floyd’s death sparked a wave of anti-racism protests across the country, including in Chicago.