Hyderabad, May 25 : Municipal authorities in Hyderabad on Thursday began an investigation after citizens in some areas in southern part of the city complained of strong and unusual odour since early hours of the day. People in Mangalhat, Begum Bazar, Tappa Chabutra, Jiyaguda, Darussalam, Chaderghat and Malakpet complained of strong smell like that of chemicals or gas. Panicked residents in some localities spent sleepless night. Some people even complained of symptoms like headaches, nausea and respiratory discomfort. Many people took to social media to voice their concern about the potential health hazard and tried to draw attention of the authorities. Greater Hyderabad Municipal Corporation (GHMC) has initiated action on the complaints by the citizens. Since residents in areas along Musi River complained of unusual odour, GHMC authorities collected water samples from the Musi and sent the same for analysis. The municipal authorities suspect that the odour could be linked to pollution in Musi. Dr Srikanth Reddy, Additional Medical Officer of Health (AMOH) visited Musi, collected water samples and sent them to Pollution Control Board for analysis. Officials said they were waiting for the results. /IANS