Most zoos around the world reverse night and day in nocturnal houses, but this limits the animals' size and their environment. But in the tropics, most of the animals are nocturnal.

''We have found ourselves in a virtually unique position. We have the climatic conditions to do this project - you need darkness to get the animals active and you ought to have a similar environment,'' said zoo executive director, Bernard Harrison.

''In temperate climates, for example, when darkness does fall early the temperature drops.

''Also, such a project is expensive, and if you can't show the nocturnal animals for half the year because it doesn't get dark until 10 or 11 pm, you'll lose money.'' Only a handful of zoos worldwide fall into the equatorial belt where night falls at a regular time, and Singapore is one of them.

Zoo executive chairman, Dr Ong Swee Law, said: ''Some of the very large habitats, where animals are free to roam under unobtrusive lighting and the vegetation has, for the most part, been left in its natural state, will give the visitor a feeling of actually travelling through a jungle under bright moonlight.'' At present only about 10 per cent of the animals the zoo intends to display have been put into their new homes. When the S$60 million (HK$286 million) project - financed by the government and the Singapore Tourist Authority - opens its doors, the zoo expects to have 1,200 animals in 47 habitats.

When the doors open for the first year's expected 600,000 visitors, they will board a tram which will take them to many of the exhibits but allow them to get on and off to follow several paths.

This attendance figure may be underestimated, as the zoo itself attracted 1.35 million visitors last year.

The zoo's visitors are 65 per cent Singaporean. The rest are tourists. The Night Safari, however, hopes to make it a 50/50 split. With the vast majority of the new animals from Asia, many of them endangered, more Asian visitors are expected.

''We'll be attracting people with package deals, like dinner evenings, and pushing tours through tour operators. Our main selling point will have to be reinforcing that experience of a tropical jungle,'' said Mr Harrison.

He sees the natural environment with the offer of dinner at the end of an evening a great attraction for Hongkong visitors.

The animals will be in specially designed enclosures similar to their natural habitat and separated from the public by strategic moats, cattle grids and discreet natural walls.

Other animals, like some species of deer, will be allowed to roam free around the forest, and are expected to congregate at night at artificial water-holes.

It will still be night when the animals become active but British theatre lighting designer Simon Corder has been brought in to provide effective illumination.

All the exhibits will be lit using low intensity but nevertheless adequate lighting.

''It wasn't an easy balance, keeping the animals convinced it was night and letting the visitor see them. So far we've found it takes the animals only two or three days to get used to the lights and accept it still is night,'' said Mr Harrison.

From a starting point in the ''Himalayan foothills'' the tram moves down to a ''Himalayan marshland'' environment, where nocturnal birds squat in their new homes.

''I didn't think swans were nocturnal'' says one member of a tour party. ''They aren't really,'' laughs Mr Harrison, ''but we have to have some poetic licence.'' Further on are wild Indian water buffalo, which are tame compared to the African variety, explains Mr Harrison.

Jackals fighting over food just thrown into their enclosure are highly active compared to their slumbering vegetarian neighbours - two Indian one-horned rhino.

''There are only about 600 of these left in the wild,'' Mr Harrison says.

Conservation is another aim of this park. ''In the long-term it's a very important angle,'' he says.

''We are actually putting together quite a group of endangered Asian animals and, given these facilities and expertise, we hope to do some captive breeding in the future.'' The zoo has already successfully bred many endangered species, and for Mr Harrison it will be an important part of the Night Safari's raison d'etre.

''People come and see our other endangered species and pay for it. It's a viable business and we expect the Night Safari to be even more successful - after all, it is unique.'' The Night Safari will be open to visitors from June 1994 between 6.30 pm and midnight.

How to get there Singapore Airlines has direct flights to Singapore daily. Cost: $6,660 for a standard economy class return. Visa: required for some nationalities.