SINGAPORE - The late Mr Lee Kuan Yew's contributions in the unions helped make Singapore what it is today, Prime Minister Lee Hsien Loong said on Friday.

The elder Mr Lee had started his political career in the unions, fighting for postal workers in 1952 and leading them in a successful strike, said the Prime Minister in his May Day Rally speech, the first since Mr Lee Kuan Yew died on March 23.

Singapore's founding Prime Minister had been engaged and passionate in his fight for workers and their livelihoods, leading rallies along with fiery speakers in stadiums packed with sweaty bodies.

"If you watch his speeches, you will find not a gentle, elderly uncle, you'll find a fierce, powerful mobiliser. You don't want to be the target of his speech," said PM Lee, to murmurs of laughter.

He added that because of the late Mr Lee, the May Day Rally is today held in an air-conditioned theatre.

"It's a completely different world," he said, addressing some 4,000 unionists, employers and government officials at The Star Performing Arts Centre,

Recalling the euologies delivered at the funeral service for the elder Mr Lee, PM Lee also said that one in particular stood out for him - the speech by trade unionist G Muthukumarasamy.

"At the state funeral service of our founding Prime Minister, that a daily rated employee union leader can stand tall, equal with all the others, and speak about how Mr Lee changed his life and share personal stories of Mr Lee with pride, it reflects the sort of man Mr Lee was," said PM Lee.

His voice choked with emotion, he continued: "The kind of society he built, and the equality and respect he fostered among citizens, working together to improve lives for all."