The opposition Jamaica Labour Party swept to an upset victory Thursday in the Caribbean country's parliamentary elections.

As vote counting continued late into the night, the Jamaica Labour Party (JLP) was leading with 33 constituencies to 30 for the ruling People's National Party.

Included in the list of JLP winners is Olympic silver medallist Juliet Cuthbert.

It was a shocking upset for Prime Minister Portia Simpson Miller's People's National Party, who won the December 2011 elections 42-21.

Days before the elections the PNP was expected to win, but the JLP gained momentum as the elections drew closer.

Only 47.5 percent of the over 1.8 million registered voters went to the polls, the lowest ever in the history of parliamentary voting in the country, despite the addition of nearly 200,000 new voters to voter lists.

A more formal count will be done Friday and it is expected that a number of those losing by small margins will seek recounts which might take weeks.

Delano Franklyn, a senior spokesman for the ruling party, said that while it ran an "organised campaign, the voters have decided to support the JLP and we respect the views of the Jamaican people and we respect the fact that the JLP has won the elections."

Prime Minister designate Andrew Holness told thousands of jubilant JLP supporters that their victory was not the end of the journey but the start of change.

"This victory shows the strength of the Jamaican democracy," said Holness.

Holness said his government would "not be government as usual, we are going to change the way we do things. We are given stewardship, we have not won a prize."

In her concession speech to a somber crowd Simpson Miller hinted they would not go quietly and urged diligence at the official counting of the ballots which takes place on Friday.