Reports I've seen suggest 1.4 to 2.5, but it's early days. Essentially if the R factor (number of people infected by a single case [0]) is less than 1, it'll die out, otherwise it'll grow.
However, that's very simplistic; one would like to think the R factor would be lowered by better hygiene.
Separately, it seems that (unlike say Spanish Flu) this tends to be worse for people who have pre-existing health issues.
There is concern that possibly people who are asymptomatic could still be infectious.
Time will tell. One number (that'll take quite some time to even have a stab at) is the mortality compared to, say, common flu.