Singapore's current status for the coronavirus outbreak is Yellow - which generally means that life can go on as normal on the whole.
But Health Minister Gan Kim Yong said on Tuesday 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 pandemic.
The Dorscon, or Disease Outbreak Response System Condition, is part of Singapore's pandemic preparedness plan that describes the current situation and what has to be done.
In the colour coding system, Green means there are just minor problems.
Yellow - the status now - refers either to a mild infection, or a severe infection that is not spreading here, but about which the community needs to be careful.
Orange means the disease is severe with transmission, but is generally contained, and has moderate to high public health impact - as was the case with severe acute respiratory syndrome (Sars) in 2003.
Some have argued that with seven local residents infected here, Singapore is already in Orange.
However, the Ministry of Health (MOH) has said the Dorscon categories are not cast in stone, but are general guidelines for action.
So even though Singapore is at Yellow, some of the measures implemented, such as quarantine and temperature screening, are actually Orange measures.
The reason Singapore has not officially moved to Orange is because there is now only one cluster which, if contained, could stop the spread of the virus here, said MOH.
But even at Yellow, the Health Crisis Management Group meets daily to coordinate medical and operational responses.
The purpose of the Dorscon measures is to delay or limit the spread of the disease in the country. Moving to Yellow already alerts the whole of government to stand ready. To handle the current crisis, Singapore has gone a step further and set up a high-level multi-ministerial task force to coordinate a whole of government response.
However, to succeed, every person has to do his or her part, said the authorities. Official measures alone, no matter how stringent, will not be enough.
So far, most of the 28 people who were infected had sought medical help.
The Singaporean tour guide who had accompanied a group of Chinese tourists to the popular Yong Thai Hang medical hall had no signs of illness, but when she heard that two saleswomen from the shop had fallen ill, she went to the National Centre for Infectious Diseases.
Tests showed she had the virus.
Mr Gan said on Tuesday: "We continue to be vigilant for more cases. There may be more with exposure to this particular travel group."
The health authorities said others who have had close contact with visitors from China, especially if those visitors appeared unwell, should monitor themselves and see a doctor if they feel ill.