The rising number of illegal immigrants from South Asian countries is related to several people-smuggling activities in the city, according to police.
The number of non-Chinese illegal immigrants arrested across the city rose sharply to 3,819 last year from 1,984 in 2014.
The marine police unit's Andy Chan Tin-chu said the poor economy in countries like Bangladesh, Vietnam and Pakistan and illegal job opportunities in Hong Kong were bringing people to the city.
He said the rise in the number of arrests over the past few years was due to stricter police action.
Chan added it was possible some South Asians learned about a change in the immigration law, so they made a "last train" move to Hong Kong to make money through illegal work, such as cleaning and delivering.
"Recently, there was a rumour that the Hong Kong government would change the law and no refugee visas would be granted to illegal immigrants, who would be deported immediately," Chan said.
Smugglers arranged a one-stop service to bring people from their home countries to the city via the mainland, according to Chan. He said some smugglers had triad backgrounds.
South Asians who intended to move to Hong Kong were normally charged HK$5,000 to HK$50,000, including air ticket and visa application, for the one-stop service.
The police will take further action and overseas cooperation to curb people-smuggling in the city by tracking down those responsible.