Two sewer mysteries unfolded overnight Friday in Brooklyn. Police say two groups of people were seen exiting manholes in Williamsburg and Gravesend.

The incidents, around an hour apart, happened at opposite ends of the borough.

Eight people were caught on video entering the sewer system at around 1 a.m. at Heyward Street and Bedford Avenue in Williamsburg, according to police. They say the group exited the sewer a short time later and took off in a car.

About an hour later, seven people mysteriously emerged from the sewer system in Gravesend near McDonald Avenue and Collin Place. Police say it is unclear how long the group was in the sewer system or what they were doing there.

Surveillance video from the Flatbush Scoop shows the Gravesend group exiting the manhole one by one before gathering near two parked cars, where they appear to remove their soiled clothing and clean themselves off.

A large police scene took over the Williamsburg neighborhood Friday evening, where emergency service vehicles and officers flooded the street.

Officers were captured on Citizen app video working to unravel the Gravesend mystery on Friday afternoon.

It's unknown if the two mysteries are connected as of Friday evening.

The NYPD's 62nd Precinct posted on X about the Gravesend mystery, saying the area is "safe and free of hazards," and the Department of Environmental Protection issued a statement.

DEP Statement:

"DEP has inspected the sewer infrastructure at this location and found no damage to the system. DEP works closely with our public safety partners to help ensure the safety and security of critical infrastructure throughout New York City. Entering the sewer system is both illegal and extremely dangerous. 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."

Friday morning's mysteries follow a man's overnight disappearance into the sewer system in Dyker Heights around six months ago.