PM Thaksin Shinawatra among supporters on a campaign stop in Bangkok, February 5. (AP Photo)

Thailand's Prime Minister Thaksin Shinawatra is expected to win an historic second term Sunday, as an estimated 44 million people head to the polls.

Twenty political parties have put up 2,289 candidates for the polls, but only four or five parties are expected to win seats in the 500-member House of Representatives.

Thaksin is confident his Thai Rak Thai party can win 350 seats. If that happens, parliament will lose its ability to censure ministers and the prime minister would have a free hand to amend the country's constitution.

Thai Rak Thai won 248 seats in 2001.

Critics say such an outcome would result in an elected dictatorship, but Thaksin defended his popularity saying, "Where in the world is a single-party government called a dictatorship? What's wrong with it when people have faith in me?"

During his first four years in office, Thaksin, 55, led Thailand to economic recovery. If re-elected, he's pledged to eliminate poverty.

Thaksin, who ran a successful telecommunications empire, is one of the richest people in Thailand.

(with files from Australian Broadcasting Corporation)