In an attempt to limit the spread of the virus, all non-essential stores in Britain have been closed since March 24. However, the government has said online businesses should continue to operate.
Boohoo said it had seen improved year-on-year sales growth during April after a marked slowdown the previous month.
However, it cautioned that given the uncertainty generated by the COVID-19 pandemic, it could not provide guidance at this stage for its new financial year ending next February.
Boohoo sells own-brand clothing, shoes, accessories and beauty products targeted at 16 to 40-year-olds.
Its shares were up 5.9% at 0816 GMT.
Britain's store-based retail sector, outside of food, has been severely hit by the lockdown to counter the pandemic, with already weak players such as Laura Ashley, Debenhams and Oasis Warehouse all falling into administration over the last month.
"Boohoo is well placed to gain further market share in these difficult times," said analysts at Jefferies, noting that in lockdown consumers are spending considerably more time on social media, a key strength of the retailer.
"Boohoo has the ability to protect its business and look for expansion opportunities," they said.
Boohoo's main UK rival, online player ASOS, also took a big hit in March; it said on April 7 its sales had plummeted 20-25% in the previous three weeks. It raised 247 million pounds of new equity and extended debt facilities to shore up its finances and help get it through the crisis.
ASOS has yet to give a further update for April sales.
The current crisis has overshadowed a stellar 2019-20 year for Boohoo. Group revenue soared 44% to 1.24 billion pounds, with UK sales up 39% and international up 51%. Core earnings (adjusted earnings before interest, tax, depreciation and amortisation) rose 50% to 126.5 million pounds.
The company said it had analysed a range of scenarios for differing levels of demand as it looks to weather the pandemic and the possibility of warehouse closures.
Having stress-tested its liquidity in these scenarios it was comfortable it had sufficient financial headroom, pointing to a largely variable cost base, low cash burn rate and 241 million pounds ($297 million) of net cash on its balance sheet.
Founded in Manchester, northern England, in 2006 Boohoo has expanded rapidly, listing its shares in 2014. It bought the PrettyLittleThing and Nasty Gal brands in 2017 and MissPap, Karen Millen and Coast in 2019.
($1 = 0.8121 pounds)
(Reporting by James Davey; Editing by Louise Heavens and Pravin Char)