Her comments come just hours after Boris Johnson announced social gatherings will be restricted to six people from Monday in the country.
Speaking on ITV's Peston show, Dr Jenny Harries compared the rates of coronavirus transmission in the UK to countries in Europe.
She said: "Our concerns are, if you look abroad, for example to France and Spain, about four weeks ago, you can see the same patterns of transmission there, and these are now starting to change through into hospital admissions and cases in other age groups than the elderly and the more vulnerable.
"So, it's really important that we take action now," Dr Harries added.
When asked about how soon we would be able to gauge whether the government's new restrictions on meeting people were working, Dr Harries said: "The incubation period of the disease is up to about two weeks, so a two-week look at something, an intervention and seeing how it's working is always a good starting place."
She added: "But the data around testing and tracing is reviewed on a daily basis to see where cases are rising, and you will have seen that in Bolton for example quite rightly where there has been a very sudden increase in cases, particular action has been taken with support of the local director of public health there.
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Dr Jenny Harries continued: "So I think we'll be watching, I think it will need a few weeks for us to see what is happening on a country basis, and also for people to get used to these new rules as well, and to really fit them into their daily lives."
As there has been an increase in people booking coronavirus tests, the government has been under increasing pressure to improve its testing system after reports some people were being asked to travel 100 miles for a test.
Earlier on Wednesday, Health Secretary Matt Hancock denied the testing system is failing, but suggested around 10% of people having to travel more than 22 miles for a test.
When Peston asked Dr Jenny Harries about people struggling to being able to get tested, she said: "I do recognise there are some people who have been offered tests in distant places and clearly that's very disappointing."
"What we want to do is ensure that colleagues in NHS test and trace continue to provide a service and we do want people to get tested."
Dr Harries continued: "The important thing is that those who have symptoms, so whether it be a fever, a new continuous cough or a loss of sense of taste or smell do apply online or by the testing number to have a test, and ...that people who don't have those symptoms only have tests when they are advised to do so by a clinician or by NHS test and trace."