Authorities are investigating multiple unusual incidents in Brooklyn after more than a dozen people were spotted climbing into and out of sewer manholes, police said Friday.

According to investigators, at least seven individuals were seen entering a manhole near McDonald Avenue and Colin Place in Gravesend at approximately 11 p.m. Thursday. The group remained underground for several hours before resurfacing around 2 a.m. Friday.

“Authorities conducted a thorough investigation following reports of unauthorized individuals inside the sewer system on McDonald Avenue,” read a social media post from the 62nd Precinct. “The NYPD and other agencies have completed their sweep, confirming the area is safe and free of hazards.”

In a separate incident roughly eight miles away, officials said another group of eight people descended into the sewer system near Heyward Street and Bedford Avenue at about 1 a.m. Friday.

Police said those individuals emerged from the manholes shortly before 4 a.m. and then left the area in a vehicle.

The NYPD’s K-9 unit, the FDNY, and the city’s Department of Environmental Protection responded to the scenes and conducted inspections.

A spokesperson for the Department of Environmental Protection said both sewer locations were examined and determined to be structurally safe, while stressing that members of the public should never enter the sewer system.

“Sewers can contain numerous hazards, including noxious and potentially deadly gases, unstable surfaces, flooding risks, and confined spaces. For these reasons, members of the public should never enter a pipe, drain, catch basin, manhole, or outfall,” the spokesperson said in a statement.

City Council Member Susan Zhuang praised emergency responders for their handling of the situation and warned about the dangers associated with entering underground infrastructure.

“What happened in Gravesend and Bedford Avenue this week was dangerous, illegal, and cannot be dismissed. Our sewers contain deadly gases, unstable surfaces, and serious flooding risks, they are not a place anyone should ever enter,” Zhuang said in a statement.

“To anyone tempted to explore these spaces: it is not worth your life. If you see someone entering a manhole, call 911 immediately.”

Investigators are continuing to examine both incidents and are working to determine whether the two groups were connected.