Police have cordoned off the culvert. [Photo/CFP]

Ninety-three people, including 50 foreigners, have been held under administrative detention for taking drugs at an overpass culvert in Shenzhen's Nanshan district on early Sunday, according to the official Sina Weibo account of the Nanshan public security bureau.

Another two foreigners have been detained on criminal charges on suspicion of drug trafficking.

The police received information early on Sunday that a crowd was gathering at the culvert for amusement, with some taking drugs, the post said. A total of 491 people were taken away from the scene, and 118 later tested positive for drugs.

It is believed that the people were attending a music party called "The Real Deal".

According to social networking website Douban, "The Real Deal" is the biggest underground party for electronic music in Shenzhen with the longest history, and was set up in 2012 by several foreigners.

"The monthly Tunnel Party…There are many foreigners and girls there," said Weibo user "Huodeyanlei-Liangzi".

"I passed through IKEA near the site that day. A lot of wine bottles were littered and there was a smell of wine there. It was really a bad influence," said "Nanguayueliang", another Weibo user.