Police on bicycles control a crowd on Yonge Street near Dundas on Monday. (Pras Rajagopalan/CBC)

Activists who oppose the G20 summit vow to be back on the streets of downtown Toronto on Tuesday to try to get their various causes heard.

The gay rights movement will stage an event called "Roving Kiss-In. Queering the G20," in the city's financial district.

On Monday, hundreds of protesters shut down traffic in parts of downtown Toronto, where the summit opens Saturday. They started at Allan Gardens and tried to occupy an Esso gas station at Dundas and Jarvis streets, but police forced them off the property.

A spokesperson for the Toronto Community Mobilization Network, which is co-ordinating many of the protests, said protesters targeted the station because Esso has received government subsidies without being held accountable for how its operations impact the environment.

The security buildup continues as both the G20, and the G8 summit in Huntsville, Ont., draw near. The G8 meetings take place on Friday, while the G20 talks will be held Saturday and Sunday.

Police have added a water cannon to their arsenal. Officers were testing what they referred to as a "water dispersal system" on Monday.

Thousand of police officers are expected to be deployed by the time the summit gets underway.

The heavy police presence didn't deter someone from firing a gun into the air early Tuesday.

RCMP and Toronto police officers heard the shots and saw a black car leave the scene where at least two shell casings were found in a parking lot on Mercer Street, just outside the restricted traffic security zone.

No one was injured and there have been no arrests.