A common phenomenon when taking off in high humidity and/or low air temperatures.
As air is sucked into the jet intakes or passes the wing's leading edge, it has a high velocity relatively to the aircraft's parts(ie, engine intake, wing and so on). Since the high velocity produces high dynamic pressure(in means of elementary fluid mechanic), but the sum of the dynamic, static and hydrostatic pressure for a given fluid remains always constant(Bernoulli's equation) and the hydrostatic pressure of the atmosphere depends only on weight, the increase of dynamic pressure is compensated by a drop in static pressure. Lower static pressure means, the condensation threshold for dissolved water vapour sinks, so the water vapours in the air condensate and form this fascinating fog. The same happens over the wing's leading edge.
There are a lot of photos here at a.net where you can see the same thing. A breathtaking sight indeed.