Singapore's role in the rise of China is not as large as some make it out to be, said Prime Minister Lee Hsien Loong, and instead described the island as a "bonsai tree model of what China is".

Like the miniature tree, Singapore might be "intriguing to scrutinise", but its lessons are harder to apply in a country as large as China.

But he added: "Hopefully some ineffable essence is useful to them and they take it back and transmute it and it may take root in China."

PM Lee was speaking at a dialogue with Bloomberg News editor-in-chief John Micklethwait, who asked for his views on the Asian superpower and said that Singapore has "always played an outsized role in China's development".

"I think you overstate our role," PM Lee replied, before providing the bonsai tree description at a welcome dinner for around 400 top business and thought leaders attending the Bloomberg New Economy Forum.

PM Lee said he did not think China saw Singapore as a model for reform, but added, to laughter from the audience, that they could be "intrigued as to how it's possible in Singapore to have free and open elections regularly, multi-party politics and one party remaining in power for such a long time".

"It is strange and it's not a given outcome for Singapore either," he added.

Similarly, Singapore's road map to success cannot be copied by Britain after it leaves the European Union, PM Lee said in response to a question on whether London can be a "Singapore on the Thames" after Brexit. "I don't think we'll have a London by the Merlion... Our histories are completely different," he said.

He cited how the British government accounts for about 40 per cent to 45 per cent of the United Kingdom's gross domestic product, while in Singapore, this figure is closer to 16 per cent. "To say (the UK) can become like Singapore - are you going to give up two-thirds of government spending, state pensions and national health?" he said.

"You will have to find a different way to prosper having made the decision to leave the European Union," he added. "Maybe, maybe if you look at Singapore, you might think you have some ideas that you can use, we hope so. But I don't think you can take one society's solution and just plonk it on a different society."

PM Lee also said that Singapore would do a trade deal with Britain directly, and in the meantime, it would port over similar trade allowances it has with the EU "because not much would have changed in Britain's circumstances domestically".

On whether the Singapore model can be followed elsewhere, PM Lee said that while he hopes others find the Republic interesting, its solutions may not be what they wish to apply.

He pointed out that one of the "cardinal principles" of healthcare here is that people take responsibility for it, and while the Government pays a large part in subsidies, there is still an element of co-payment unless one is very poor. "That's not a principle accepted everywhere... the national healthcare system in Britain explicitly refuses to," he said.

But he also noted Singapore is able to do this because it built its system progressively, through its Central Provident Fund.

"If you haven't built that up over a long period of development, and overnight you want to put aside one-third of income into a compulsory savings fund for your old age so you will not retire poor, I think a lot of people would get angry straightaway," he said.

The Prime Minister also tackled questions about immigration, which he said was "a vexed subject in every country".

Asked if he thought there were any countries that did immigration well, PM Lee said different countries make different trade-offs.

Some have been very open and benefited considerably like the United States, he said, adding that while immigration is now a hot political issue there, it is nevertheless important to have an environment where people can live and work and make a country vibrant.

"It is a tremendous plus that America has and which China and Japan don't have," he said.

In contrast, Japan is a much more closed, tight-knit society which is less conscious of the outside world.

"Now they have to shift that trade-off because the numbers are telling them that their population is falling," he said.

Singapore is trying to strike a "careful balance of having enough of the next generation born to us, but (with) some significant contribution from people coming in, who can cast their lot with us and become Singaporean," he said.

PM Lee was also asked what other models of governance inspire him. While no single model wouldprobably apply to Singapore, the closest one might be Venice, the Italian city which has thrived for 900 years, he replied.

"What we are really looking for is how to be a small country and have the elixir of life. In other words, to be able to adapt to change, dodge bullets and remain successful for a very long time to come," he said.

Venice is the best model, he said, and while it has not been the same after the centre of gravity shifted from Europe to the Atlantic Coast, "900 years is not a bad run".

"What we want to do is to be able to keep on reinventing ourselves as the world changes, so that 100 years from now, if the next Bloomberg conference is cancelled, it can still come to Singapore," he said, in a reference to how organisers had moved the forum from Beijing after its Chinese partner asked to postpone it.