The opposition in the Caribbean twin-island nation of Trinidad and Tobago has won a decisive victory in Monday's parliamentary election, preliminary results suggest.

The win by the centrist United National Congress (UNC) party means that Kamla Persad-Bissessar will be appointed as the next prime minister.

The 73-year-old already held the post once before, from 2010 to 2015, but her party was defeated in the last two elections by the centre-left People's National Movement (PNM).

Preliminary results suggest the UNC, which campaigned on a promise to raise wages and create employment, managed to win a number of parliamentary seats previously held by the PNM.

PNM leader Keith Rowley conceded defeat late on Monday, saying that it had not been a good night for his party and that it was clear that it had lost the election.

Rowley, 75, served as prime minister from 2015 to March of this year, when he announced he was stepping down and handing the reins of power to the 50-year-old energy minister, Stuart Young.

But rather than serving out the remainder of Rowley's term, Young called a snap election just hours after being sworn in as prime minister.

The move was widely seen as an attempt by Young to secure a stronger mandate amid criticism by the opposition that his elevation to prime minister was unconstitutional.

The election came at a time when the country is grappling with a rise in homicides and an economic slump.

The outgoing government declared a state of emergency in December, which stayed in force for 105 days.

During her campaign, Persad-Bissessar promised to raise wages for public sector workers who have been struggling to meet rising costs of living.

It was an issue she addressed again after the governing party had conceded defeat.

"This victory is for the senior citizens to keep their pensions. This victory is for public servants to get their rightful salary increases. This victory is to re-open the children's hospital. (...) This victory is once again to give laptops to our children and to create over 50,000 jobs," she told supporters who had gathered at the party headquarters.

She also assured those gathered that "no-one" would be left behind, stressing that "when UNC wins, everybody wins".