A monthly index measuring the presence of aedine mosquitoes shows they surged to 11.3% in June from 10.2% in May across Hong Kong.
However, ten out of 55 districts under government monitoring hit the third level of state warning systems with a reading above 20%, according to a press release from the Food and Environmental Hygiene Department on Monday.
The hardest-hit district is Tseung Kwan O North in the New Territories, which is near the Po Lam area, with a reading of 41% in June, up from 32.8% in May.
Tseung Kwan O was followed by Pok Fu Lam on Hong Kong Island (37.9%), Fanling in the New Territories (31.6%) and Sai Wan on Hong Kong Island (30.9%).
Lai King, Kowloon Bay, Wong Tai Sin Central, Tseung Kwan O South, Tsing Yi North and Kai Tak North also exceeded the alert level, which means around one-fifth of the area in the district was hit by the mosquitos, Apple Daily reported.
The department said it was very concerned about mosquito infestation, and an inter-departmental anti-mosquito response mechanism had been activated in areas above the alert level.
Starting from July, the department added five more districts to areas it is monitoring including Central and Admiralty on Hong Kong Island, Yau Tong in Kowloon, Wo Che, Tsuen Wan West and Tuen Mun West in the New Territories.
The department will also launch a 10-week anti-mosquito campaign in the city on August 13.
The concern is about Aedes albopictus, a species of mosquito that can transmit dengue fever and the Zika virus.