TORONTO - Protesters opposed to the G20 summit briefly occupied a gas station as they marched through downtown Toronto this afternoon.

The group of several hundred is opposed to the police buildup in Toronto in advance of the weekend summit.

They say the money spent on security could better be spent on the poor, health care or child care.

The group marched through the streets under the watchful eye of dozens of police on bicycles who blocked side streets as the marchers passed.

The noisy but otherwise peaceful protesters chanted slogans such as "Whose streets? Our streets!" and "Justice now!"

Activists have promised to be out in force to protest the two-day summit of world leaders that starts Friday.

Meanwhile, police warn they have added a water cannon to their arsenal as they step up security ahead of this week's G20 summit in Toronto.

Provincial police Const. Michelle Murphy of the Integrated Security Unit says the water projection system will be used to control large crowds if there are riots.

Toronto's police chief has said 5,100 officers have been assigned to keep the city safe as the weekend summit nears.

Officers have been doing security sweeps through parks where protests will be held and workers have put the finishing touches on the three-metre-tall fence that surrounds the security zone.

People are being advised to avoid the fenced-off area, and officers will ask those trying to get inside for identification and their reason for entering.