Health Minister Gan Kim Yong said that the situation could change to Orange if there is widespread transmission from unknown sources.
That would be just one level below Red, which signifies an out-of-control epidemic.
According to the Health Ministry, some of the measures implemented, such as quarantine and temperature screening, are actually Orange measures.
To handle the current situation, Singapore has implemented a step further and set up a high-level, multi-ministerial task force to coordinate a whole of government response.
Singapore has to date recorded 28 infections, including a six-month-old baby.