More than 500 officers raided the Our City residential complex in Pham Van Dong Street, Duong Kinh District, and found hundreds of people using foreign-made machines gamble online. 

They found more gambling machines installed in several buildings in the complex. 

Several Vietnamese employees were interrogated but not held.

Senior colonel Le Ngoc Chau, head of the city police, said it was "a huge and very complicated operation".

Built in 2009 by Chinese investors, the $85 million Our City is 43 hectares in size and mostly occupied by Chinese.

Vietnam has relaxed its stance on gambling, legalizing sports betting in 2017 and allowing people aged over 21 with a monthly income of at least VND10 million ($445) to play in a casino on the southern Phu Quoc Island on a pilot basis.

But online betting remains illegal. Gambling and organizing it can attract fines of VND10-50 million ($430- 2,150) or fetch jail terms of three to seven years.