The firm said work is currently underway at its Barnsley warehouse to increase the stockholding capacity through the construction of an additional mezzanine.
This will increase capacity by a further 10 per cent to 22 million units and is scheduled to complete by the end of April.
Pre-tax profits jumped to £29.9m in the six months to February 28.
UK retail sales rose 22 per cent to £414.5m, while international sales increased 28 per cent to £716.8m on a constant currency basis.
Chief executive Nick Beighton said: "These results show strong trading at the same time as we are making substantial investment in our future.
"Alongside our investment in our people and our technology, we are accelerating investment in our distribution and logistics, laying the foundation for £4bn of net sales."
The group kept its guidance for full-year sales growth of between 25 and 30 per cent.
The firm raised its spending guidance for the full-year for the second time in less than three months and now expects capital expenditure of between £230m and £250m.
Analysts said the investment plans highlighted the costs faced by online retailers.
Russ Mould, investment director at AJ Bell, said: "This offers a reminder that, although not burdened with the same level of overheads as traditional retailers, it does incur material costs on items like distribution and logistics."
Asos has spent just over £95m so far this year, with around half on technology and transformation programmes and the remainder on infrastructure across its supply chain and head office.
The firm said the heavy investment is bearing fruit, with shopper visits to its site up by 25 per cent year-on-year, average orders up 8 per cent and a 2 per cent rise in the average basket size.
The group said it is confident that by concentrating on successfully executing its investments, it is positioning Asos to be the world's number one destination for fashion-loving 20-somethings.