A nurse from Beijing has reportedly said there are over 90,000 cases of it in China. With the Chinese government isolating more cities and actually having the military surround Wuhan to make sure no one gets in or out. They are taking pretty severe steps if there is less than 3,000 infected as they claim.
If 90,000 are already infected a quarantine will not work. Only option is to cease all air travel from China at this point and it’s probably already too late for that.