The violence came amid growing calls for the resignation of Thaksin Shinawatra, the prime minister, who called the snap elections three years early in an effort to reassert his mandate.
Police said the first bomb exploded at the entrance of a school used as a polling station in the largely Malay-speaking district of Joh Airong on Sunday, wounding two soldiers carrying ballot boxes to a car.
A second bomb exploded at another polling station 2km away and wounded two policemen, they said.
Preliminary results from the Election Commission were expected to trickle in throughout the night, with a final tally likely on Monday morning.
Facing an opposition boycott, Thaksin Shinawatra had turned the poll into a referendum on his leadership by pledging to quit if his Thai Rak Thai (Thais Love Thais) party wins less than 50% of the ballots cast.
That is unlikely to happen as rural Thais, who have benefited from handouts to their villages and cheap healthcare during Thaksin's five years in office, looked set to return him with another large majority.
But the boycott meant that the result is almost sure to fall short of a constitutional requirement that all 500 parliamentary seats be filled before a new government can be formed.
Somjai Phagaphasvivat, a political scientist, said: "The poll will produce a protracted deadlock for months. The final outcome is far from certain."
The crisis is already taking its toll on the economy, paralysing decision-making in business and sapping the Thai stock market, Southeast Asia's second-worst performing bourse after Malaysia this year.
"The poll will produce a protracted deadlock for months. The final outcome is far from certain"
Somjai Phagaphasvivat, political scientist
The opposition and the People's Alliance for Democracy, an ad-hoc group bent on forcing Thaksin out, had urged voters to tick the abstention box on ballot papers as a vote against the Thai leader, whom they accuse of corruption and abuse of power.
Thai Rak Thai candidates ran unopposed in 265 of 400 constituencies and as many as 50 could fail to win the minimum 20% of the vote they needed to record victory in an uncontested seat, casting doubt on the validity of the overall result.
Thaksin, a 56-year-old telecoms billionaire has urged his opponents to accept the results of the poll, which was open to around 45 million Thais.