Seven candidates are standing against the president, who took power after the death in 2006 of eccentric dictator Saparmurat Niyazov, but all are loyal members of the elite who have not sounded a note of criticism in the campaign.
Energy-rich Turkmenistan is promoting the elections as a new step in a programme of democratic reforms. But Berdymukhamedov's promise last summer to include genuine opposition in the polls appears not to have been fulfilled.
"Elections in Turkmenistan are the clearest evidence of the irreversibility of the democratic process," proclaimed the anchor on state television in its morning bulletin.
"Aware of their great responsibility for the future of the motherland, the people will choose the most worthy of the eight candidates," the anchor added.
The figurehead candidates running against Berdymukhamedov include Energy and Industry Minister Yarmukhammet Orazgulyev and Kakageldi Abdyllayev, the chief executive of a subsidiary of state energy firm Turkmengaz.
Other token rivals are his water resources minister and the director of a cotton factory. Another candidate, local agriculture official Redzhep Bazarov, even showered Berdymukhamedov with praise in his election manifesto.
Just under three million people have the right to vote across the vast ex-Soviet state that extends from the Caspian Sea to Afghanistan and is one of the most secretive nations in the world along with North Korea.
Polls opened at 0300 GMT and should close 12 hours later.
Berdymukhamedov has started cautious reform after the excesses of the notorious personality cult under Niyazov, which extended to installing a golden statue of himself in Ashgabat that rotated to always face the sun.
In a half decade that Turkmenistan calls the "Era of Rebirth", Berdymukhamedov had reopened cinemas, theatres and research institutes and started to encourage foreign majors to help exploit its vast energy reserves.
But critics say that the former dentist's reform drive has been little more than window dressing and that he still presides over an autocratic one party state that brutally cracks down on dissent.
"Serious human rights violations such as torture and ill-treatment continue to be committed in detention facilities and severe restrictions remain on freedom of movement and expression, political activism, faith and many other fundamental rights," Amnesty International said in a statement ahead of the polls.
Berdymukhamedov in July promised to open the elections up to the exiled opposition, a vow that mysteriously came days after a series of blasts outside Ashgabat blamed on a fireworks depot fire that left 15 dead.
But none of the opposition leaders in exile took up the offer, saying they were sure of immediate arrest if they dared return to the country.
A small mission from the OSCE's Office for Democratic Institutions and Human Rights (ODIHR) has arrived in Turkmenistan for the elections but they will be making no public assessment of the polls.
Turkmenistan issued no invitation for OSCE observers to assess the elections on a full-scale mission while human rights workers and journalists have also been denied access to the country.