Where: The photographer is standing on the corner of Jubilee Street, looking east along Des Voeux Road.
The first building on the left is the Central Fire Station  - you can see the high, wide doorways to let the fire engines in & out. Today the Hang Seng Bank's HQ building is on this site.
Who: Lots of people out & about, many wearing topees (aka pith helmets) to keep the sun off.
Despite the hats, everyone is wearing a jacket, suggesting it's one of the cooler months of the year.
What: One square of the photo shows four different types of transport:
Does anyone recognise the model of car?
When: The photo was sold as '1940s', but we can pin it down to the 1930s. The first clue is those topees. On a previous photo , Barbara noted:
That the European is wearing a topee suggests the date of this photo is pre-1938 at least. When my family and I returned to HKong early that year, we were astonished to find that most Europeans no longer wore topees, as during our earlier sojourn there 1927-29 we all wore them.
Further evidence comes from another version of this same photo:
Commercial photographers often sold their photos in a variety of sizes, and cropped them accordingly. In the wider copy above, we can see the previous Central Market building  still standing on the right of the photo. That was demolished in 1937, so the photo can't be newer than that.
Working from the other direction, the large white tower in the distance belonged to the Gloucester Building, opened in 1932.
Looking even further away, there's another distinctive rooftop:
That's the dome of the Bank of East Asia building, completed in 1935.
So sometime between then and the demolition of the market in 1937 gives 1936 as a likely date for this photo.
[CORRECTION May 2013: As pointed out in the comments below, the building with the dome is the Bank of Canton, completed in 1924. So the date for this photo is somehwre between 1932 and 1937.]
Trivia: The Gloucester Building's clock says the time is twenty past two, but the clock in the '4 types of transport' photo shows ten to twelve. Which is right?