The lockdown will largely be a "general" one, meaning essential services will run and industrial activity will be allowed.
But in nine days in August, the east Indian state will go into a "complete" lockdown, with everyone required to stay indoors.
West Bengal has 60,830 cases of coronavirus including 1,411 deaths and 39,917 recoveries, according to the Indian Ministry of Health and Family Welfare, as of Wednesday.
"We need to break the chain...If we can block the virus even to a certain extent we should take whatever steps we can," Banerjee said.
"A lot of people think that the numbers are too high, but earlier we had one lab for tests, now we have 56," she said.
Banerjee added that the state's health infrastructure had improved significantly in the last eight to nine years.
India has more than 1.5 million coronavirus cases, the third highest tally in the world according to Johns Hopkins University.