BANGKOK, Aug. 7 (Xinhua) -- National referendum on Thailand's 2016 draft constitution and its additional question begins at 8 a.m. (0100 GMT) Sunday as planned. The voting process will last for 8 hours as all polling stations will be closed for voting at 4 p.m. (0900 GMT). The unofficial results will be known before 9 p.m. (1400 GMT), according to the Election Commission.