Interview question

I have 6 million co-ordinates of the type (x,y).
I know the bounding rectangle for those points,
that is I know the min(x),min(y),max(x),max(y)
on the complete range.

Now, write a function closestTen(x,y), which
will take a (x,y) point as input and find its 10 closest
neighbors in the given bounding rectangle.

This input (x,y) can be inside the bounding rectangle
or outside it. It may also be one of the 6 million points,
but not necessarily.