A manhole cover flew up from the ground near Queen and James streets, according to two security guards, and they saw two men emerge from the sewers about 1:30 Sunday morning.

The men who emerged from the manhole were joined by two others.

This is one of the stranger tales to emerge from a day of violence and vandalism on the streets of Toronto, with more than 500 people arrested in connection with G20 protests.

The security guards, who work for the Hudson's Bay in Eaton Centre, were keeping an eye on suspicious men hanging around the area on bicycles.

"My co-worker and I were just doing our patrol and checking the windows because a few of them were broken by some of protesters," one of the guards told CTV News. "As we were doing our rounds, we turn the corner and see these two guys coming out of the manhole and walking east on Queen."

The other guard said he was alarmed to see such a sight:

"All I saw was this manhole pop up, this skinny kid fly right out of the manhole at super speed, and he just took off…"

The guard said another man then popped out of the manhole.

"Me and my partner kind of froze, we freaked out saying, 'My God, what just happened?'"

The guards immediately reported the incident to authorities driving by in a court services van. They called in for police backup.

The guard said he saw about 30 to 40 police officers converge on the men.

"Perfect timing, I must say, the police just ran to the corner and waved them down ... They were here in seconds."

He said police were able to stop four people in total. "One guy kept on going, but they got him," he said.

"Let me tell you, I was so freaked out watching people coming out of a manhole cover at 1:30 in the morning. I've lived in the city for 45 years, this is just too weird."

City workers spent Sunday morning welding shut manhole covers in the protest zone, as police prepared for more possible protests and violence.