BUSAN - Singapore's next General Election (GE) may not take place "when everybody is expecting it", said Prime Minister Lee Hsien Loong on Friday.

In an interview with Singapore media, Mr Lee said the decision on when to hold the next GE - which must be called by January 2017 - will take into account a variety of factors including global and local events.

"It depends on what issues are, what the state of our preparations are," he told reporters on the sidelines of an Asean-Korea summit in Busan.

"It depends on what's happening in the world, if a major crisis is coming up then we have to clear that... It also depends on (what) other agenda we are busy with."

Noting that Singapore will mark its 50th anniversary of nationhood next year, Mr Lee added that the year-long calendar of celebrations will also have to be considered.

"We will have to take all this into account and make soundings and choose the right moment. Not necessarily when everybody is expecting it," he said.

Adding that the ruling People's Action Party is "working hard preparing" for the elections, he said: "When we're ready we will call, as soon as we're ready."