In previous attacks, acid was thrown from buildings onto pedestrians
Nine tourists and a child were among 30 people injured in an acid attack in a busy street in Hong Kong.
More than 100 people have been injured in similar attacks since December 2008 when bottles of acid were dropped from buildings in a pedestrian zone.
The latest attack was at the Temple Street night market in Yau Ma Tei when two bottles were thrown, state broadcaster RTHK reported.
The 30 people suffered light injuries and were treated in hospital.
Police were investigating, with firemen also on the scene, but no arrests had been made, AFP reported.
In December six people were injured when a bottle of acid was thrown down a street in Causeway Bay, a shopping hub which was packed with people celebrating the Hong Kong football team's victory over Japan in the East Asian Games final.
Police have previously offered 1.5 million Hong Kong dollars (£120,000; $190,000) for useful information on the attacks.
A rooftop camera network was set up over Mong Kok, the site of one attack, but has failed to catch those responsible.