St. Louis police have arrested at least 17 people for an “unlawful assembly” as activists staged a spontaneous sit-in outside a convenience store following a mass march, part of a four-day “Ferguson October” public event to protest police brutality.

Early on Sunday morning between 100 and 200 people marched on a QT (QuikTrip) convenience store at Vandeventer and Chouteau. Protesters sat down, surrounding the convenience store.

Protesters reach quik trip in the grove. #fergusonoctoberpic.twitter.com/bSnsMFDa2g — Durrie Bouscaren (@durrieB) October 12, 2014

They staged a brief a sit-in at around 1 am local time, which local police spokeswoman Schron Jackson has called an “unlawful assembly”.

Protesters sitting outside quik trip in The Grove in #STL. Police say unlawful assembly. #fergusonpic.twitter.com/MAR8NctUfT — Durrie Bouscaren (@durrieB) October 12, 2014

But according to Police Chief Sam Dotson, protesters were “attempting to storm” the store and showed “illegal behavior”.

Protestors attempting to storm Quicktrip at Vandeventer & Chouteau. All protestors engaging in illegal behavior will be subject to arrest. — Chief Sam Dotson (@ChiefSLMPD) October 12, 2014

Sam Dotson then tweeted that protesters started “throwing rocks at the police” as they were asked to leave the area.

Protestors now throwing rocks at the police. Arrests have been made for continued illegal behavior. — Chief Sam Dotson (@ChiefSLMPD) October 12, 2014

Police reportedly used tear gas and pepper spray to disperse the crowd.

But protesters say that their sit-in was peaceful.

“We were just sitting there. Police came closer and closer to us. Everybody was sitting down, linked-up, holding hands,” a female participant has told CBS.

The impromptu sit-in outside QT was part of a two day “Ferguson October” public event, which lasts through Monday.

READ MORE: 'Terror on American soil': #FergusonOctober stages 4-day rally as shooting anger rages

Mass events have been planned on October 10-13 - the “Weekend of Resistance” – after a second black man 18-year-old Vonderrick Myers Jr was shot dead by an off-duty white police officer, who reportedly fired at him up to 17 times.

READ MORE: ‘Justice for everyone!’ Thousands stand up against police brutality in Ferguson, St. Louis

On Saturday hundreds of protesters held a “Justice for All” march and rally in downtown St. Louis. The mother of Michael Brown, who was killed in the August 9 shooting, marched with a group of some 300 people on Ferguson police department.