Chief Executive Donald Tsang Yam-kuen yesterday visited the scene of Saturday's acid attack in Mong Kok to be briefed by detectives on the progress of the investigation. Mr Tsang went to the rooftop of the Yuen King Building, from which two bottles were believed to have been thrown. He was shown maps of the area, plans of the building and pictures of the containers that crashed to the ground and splashed acid over 46 Christmas shoppers. Mr Tsang stayed for about 10 minutes and left without commenting. A spokesman said the chief executive was concerned about the incident. As of last night, no arrests had been made. Dozens of officers searched buildings in the area and interviewed residents and passers-by. The acid landed near the junction of Sai Yeung Choi Street South and Shangtung Street. Forty-six people were splashed with the corrosive liquid and taken to hospitals. All were discharged on Saturday night. Police have said they believe someone threw the bottles from a height. Samples of the acid were sent to a laboratory to determine its type. Kowloon West regional commander Tang How-kong said the investigation was difficult because the attack appeared to have been random. Yesterday, the pedestrian area of Sai Yeung Choi Street South was again swamped with shoppers. Some said the incident did not bother them, but others expressed hope the attacker would be caught soon. Yau Tsim Mong district councillor Henry Chan Man-yu said building managers should step up security. 'The problem is that there are too many commercial-cum-residential buildings in the district and many people go in and out every day,' Mr Chan said. He suggested caretakers or building managers should register visitors or set up more surveillance cameras. But residents of Yuen King Building said it was difficult to check all visitors because there were guesthouses, clinics and beauty salons in the building. Police asked the public to call a special hotline, 2398 6200, if they had information about the attack.