Singapore has invested heavily in public housing, transport infrastructure and training its citizen workforce to raise manpower productivity in recent years.These efforts are complemented by welcoming talent from all over the world to make Singapore "a vibrant economic hub", Mr Lee said.However, he stressed that immigration will have to be politically sustainable for Singapore."Sustainable means we can handle the numbers, that we can integrate them into our society," Mr Lee said, "meaning our people are able to adapt to the inflow, and the new immigrants are not so overwhelming that they dilute our core and our values, our ethos of society."He also said immigration must meet Singapore's practical needs in terms of lifting its low birth rate, and fulfil the country's economic imperatives."Because we'll need that range of skills and experiences and talents which no society can generate on its own," Mr Lee said. "You have to get that from all over the world -- Europe, America, China, India. Wherever there are people who have something special to contribute, we think we have to see how they can fit in to Singapore."