Her report for the government says neglect to town centres and online shopping has left many “dying”.
Portas said: “The model of the high street is so outdated. It is working in the same way that it did in the 1960s, but the 1960s are no longer here.
“Many [high streets] are sickly, others are on the critical list and some are now dead,”
She is recommending relaxing rules for market stalls to make it easier to set up stands, cutting regulations for High Street traders and introducing a national market day.
Vacancy rates in market towns have doubled in the past two years due to the economic downturn.
A report this summer found that one in 10 town and city centre shops stood vacant at the end of May.
But Matthew Hopkinson of the Local Data Company (LDC) pointed out that “not all High Streets are in crisis”, with some town centres having low shop vacancy rates.
Richard Dodd, from the British Retail Consortium said: “It seems that there are a good number of sensible ideas in the report which, if taken together and adopted, could make a difference to many of our troubled high streets.
“Clearly a national market day is never going to be the sole solution but alongside a range of other measures it could make a useful contribution to generate interest and stimulate shop numbers, adding to the originality and distinctiveness of particular town centres.”