About 50 million voters will answer 'yes' or 'no' to the question -- Do you accept the draft constitution? They are also being asked a supplementary question, whether or not the appointed senate should be allowed to join the lower house in selecting a Prime Minister.
If the majority of voters say 'yes', the draft becomes the Constitution, enhancing the military government's legitimacy in the run-up to an election which Prime Minister Prayuth Chan-ocha, who led the 2014 coup, has promised will happen next year.
Prime MinisterPrayutand other key government figures openly announced a couple of days back that they would vote "Yes" in today's referendum.
The military junta which took power after a coup in 2014 called for the Constitution to be rewritten to ensure "clean politics" in the country. The referendum is likely to be a judgement day in Thai politics.
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Not only will the fate of the new draft Constitution will be determined, but the outcome could also be significant for entities such as the military-created National Council for Peace and Order (NCPO) and politicians from different parties.
The way this referendum has been run by the military authorities has been widely condemned by human rights groups because of the ban on campaigning, which has seen dozens of people detained and charged.
As a result, public knowledge of the draft Constitution is limited.
If it is approved, the military government has promised that a general election could be held by late next year, restoring democratic government.
But critics have argued that the draft will perpetuate army control with the armed forces and an appointed senate retaining decisive influence over future elected governments.
However, the explosion caused by the 15 kg bomb shattered glass windows of some houses nearby. Whether the blast was connected to the voting in referendum was not known.
The motorcycle bomb comes after the blasts that destroyed 19 roadside power posts in nine districts of Narathiwat last night. Police were investigating the incidents.
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"The NCPO should reveal when exactly in 2017 the election will take place and make sure all of the process is transparent and inclusive. Otherwise, pressure from outside will not go away," Virot said.
The political scientist said a majority "No" vote would hopefully be a wake-up call to the NCPO, telling it to review itself and improve.
"(But) I'm not very sure the NCPO would do that," she was quoted by the Nation as saying.
"So, conflicts are very likely to persist. That's one thing I see for sure," Chalidaporn said.
Former prime ministerYingluckShinawatra has urged voters to turn out and "choose what direction the country should take in the future".