Tesco saw group operating profit before exceptional items fall by 54.6% to £354 million in the 26 weeks to August 29.
UK like-for-like sales declined 1.1% with overall group sales 1.9% down on the corresponding period in 2014/15.
UK and Ireland profits before exceptionals were down from £543 million to £166 million.
But chief executive Dave Lewis was upbeat, suggesting that the supermarket group was on the road to recovery.
Lewis said: "We have delivered an unprecedented level of change in our business over the last 12 months and it is working.
"The first-half results show sustained improvement across a broad range of key indicators.
"In the UK, we continue to improve all aspects of our offer for customers resulting in volume growth which is allowing us to create a virtuous circle of investment."
Connor Campbell, analyst at spreadex.com, said: "A worse than forecast fall in profits, from £779 million to £354 million, greeted Tesco investors this morning, alongside a 1.1% drop in like-for-like sales that was somewhat mitigated by a 1% increase in its international sales.
"After a surprisingly strong set of results from Sainsbury's last week, with the orange supermarket's better than expected full year outlook causing a sector-wide surge, Tesco's figures have arrived to remind everyone the biggest of the big four is still in the midst of an unenviably tough period."