New Line in a formula

I'm trying to fetch data from multiple cells, and put it all in one cell. I use the following to get the label and data, but I need to put a hard return to move to the next line for the next label/data pair:

=a1&": "&a2 {hard return}
&b1&": "&b2 {hard return}
...
Where a1 and b1 are labels, and a2 and b2 are data.