At least 800 undocumented immigrants, including 377 Bangladeshi nationals, were detained during a special operation conducted by Malaysia's Immigration Department in Bukit Bintang area, media reports said on Wednesday.

The integrated "Ops Belanja" operation, conducted from 7:30pm to 10:30pm, targeted undocumented migrants following weeks of public complaints, Immigration Department Enforcement Division Director Basri Othman told The Daily Star.

During the raid, officials also uncovered an online gambling den.

A CCTV was also present at the venue to monitor the situation.

"When the authorities broke down the door of the premises, seven foreigners were still busy engaged in online gambling, unaware of the presence of the operation personnel. They were all detained," Basri said at a press conference after the raid as quoted by The Daily Star.

Checks were conducted on 2,445 individuals, including 1,600 foreigners and 845 locals, he said.

The detained individuals were aged between 21 and 65.

They were shifted to Putrajaya Immigration Department for initial screening before being placed at the Bukit Jalil and Lenggeng Immigration Depots for further probe into the incident.