City workers using metal detectors found several razor blades Monday at a popular playground along San Diego's Mission Bay, officials confirmed.

The search was sparked by the discovery of six razor blades in Bonita Cove Park over the weekend. The blades, which appeared to be brand new, were found facing upwards by city workers around 12:15 p.m. Sunday.

The park was closed but reopened again around 2:30 p.m. No children were injured.

San Diego Police did not release how many razor blades were found Monday. They immediately put up caution tape once again, blocking off the public's access to the playground.

This is not the first time razor blades have been discovered at Bonita Cove Park. On Sept. 13, three were found at Mariner’s Point. They were pointing upward and appeared to be planted there on purpose.

On April 30, two boys were cut by razor blades while playing in the grass. In that case, nearly 20 razor blades were found scattered in the area.

Razor blades were also found in Bonita Cove Park multiple times in 2013, including one instance where a mother was injured. SDPD Lt. Scott Wahl estimates there have been about a half dozen cases in the last several years.

He said it is very difficult to investigate because the incidents are spread out, with four to six months in between each.

Efrain Estala was heading to the playground Sunday with his children when he saw the police cars. He was immediately concerned that someone had once again planted razor blades.

"It's pretty sad that actually somebody is going to take the time to try to hurt kids around here," Estala said.

To date, no arrests have been made.

Lt. Wahl said short of putting someone at the park for a 24-7 watch, police are depending on the community's help to solve the case. If you know anything about these incidents, call Crime Stoppers at 888-580-8477.