Singapore will hold a general election on September 11, more than a year before a deadline for the next polls, the office of Prime Minister Lee Hsien Loong said on Tuesday, seen riding the feel-good factor of the city-state's 50th birthday.

Analysts have said the People's Action Party (PAP), which was founded by the prime minister's father, the late Lee Kuan Yew, and has ruled since six years before independence in 1965, will be keen to tap national pride the Aug. 9 celebrations generated and improve on its performance in the last election.

In 2011, the PAP won its lowest ever share of the vote with many people unhappy about the cost of living and immigration.

Those issues will again be at the forefront of debate when candidates from the PAP and opposition parties head to campaign rallies across the affluent city-state.

The next general election had to be held by January 2017, but there had been speculation in the media and political blogs that it would be called early.

"Soon I will be calling elections to ask for your mandate, to take Singapore into this next phase of our nation building," Lee said in his annual speech as part of the National Day celebrations.

The legacy of Lee Kuan Yew, Singapore's first prime minister, who died on March 23, will be fresh in the minds of voters and the PAP will be keen to convince people it is best placed to ensure Singapore's success over the next 50 years.

The elder Lee oversaw the city-state's rapid rise from a British colonial backwater to a global trade and financial centre and his death triggered a flood of tributes.

In his lifetime, Lee drew praise for his market-friendly policies, but also criticism at home and abroad for his strict controls over the press, public protest and political opponents.

Under Lee, political opposition and independent media were not allowed to flourish in the same way as the economy, a state of affairs that persists to this day.

Singapore placed 153 out of 180 countries in the latest World Press Freedom Index.