The two parties with the most votes will contest a second round on October 18, with Tshering Tobgay, 52, educated at Harvard, hoping for a second consecutive term as prime minister.
But the Mountain Cyclist's People's Democratic Party (PDP) faces a tough challenge from the Druk Phuensum Tshogpa (DPT), winner of the first Bhutan election in 2008, and two other parties.
The 800,000 inhabitants of Bhutan the size of Switzerland obtained television in 1999 and democracy came only in 2008 when their "dragon kings" yielded absolute power.
But it has tried to protect itself from the disadvantages of modernization, fighting for Gross National Happiness, being carbon-negative and reducing the number of tourists with a daily rate of $ 250 per visitor in high season.
Opinion polls are banned and analysts are few, but one observer told AFP that the PDP had an advantage over its handling of the economy, with strong growth and low unemployment.
However, corruption, rural poverty, youth unemployment and the prevalence of criminal gangs remain a challenge.
"I think the central issues in 2018 are the same as in 2013 and 2008: the economy, rural development, infrastructure and, to a certain extent, tourism," Tenzing Lamsang, editor of the Bhutanese newspaper, told AFP.
Bhutan relies heavily on its neighbor, India, for help, investments in infrastructure, imports and as an export market, particularly for the electricity it generates using hydroelectric power.
During the last election campaign in 2013, India abruptly withdrew subsidies on imports of kerosene and cooking gas, in what was seen as an attempt to guarantee a change of government.
India is not happy with China's growing influence in Bhutan. Last year, India and China were involved in a military confrontation on the Doklam plateau, high in the Himalayas, claimed by both China and Bhutan.
India itself does not claim the territory but has a military presence in Bhutan. He intervened to prevent the Chinese border guards from building a highway there, which led Beijing to accuse it of trespassing Chinese territory.