Warner Bros is on the cusp of crossing the $1bn domestic milestone as it launches Harry Potter And The Half-Blood Prince around the globe.

Sources said they expected Warner Bros would make the announcement on Wednesday [July 15], however the studio declined to comment as executives busied themselves with last minute preparations for the sixth entry in the family franchise.

Riding high on excellent reviews in the US – critical opinion has been more polarised overseas – Harry Potter And The Half-Blood Prince was set to open in approximately 3,000 midnight screenings across North America on Wednesday. By the end of the weekend it will have launched in roughly 4,300 theatres.

The film is expected to dominate the box office for several weeks and conservative estimates have forecast a five-day weekend in the $140m region.

In the end it could be considerably higher. Harry Potter And The Order of The Phoenixgrossed $139.7m in its first five days in July 2007, and anticipation for the follow-up has been mounting ever since Warner Bros pulled the film from last autumn’s release schedule to ensure it had a viable summer blockbuster candidate.

To date every episode in the highly profitable series has taken more than $249.5m domestically, with Philospher’s Stone setting the high-water mark of $317.6m by the end of its run in February 2002.

Overseas, each film in the franchise has consistently scored more than $546m and a soaring international run would appear to be on the cards yet again as Warner Bros Pictures International aims to join its domestic counterpart in the $1bn club. Harry Potter And The Order Of The Phoenix set the overseas record of $646.2m two years ago.

The film debuts in the UK, Japan, Australia, France, South Korea, Spain, Italy and Brazil on Wednesday as a prelude to the company’s biggest day-and-date conventional and IMAX release yet. By the end of the first weekend it will have opened in more than 14,000 screens in 54 markets including all the majors, accounting for roughly 85% of total markets.

In terms of total franchise revenue, Harry Potter has amassed roughly $4.5bn in global receipts and will overtake James Bond’s $5bn running total within days to become the biggest film series in history.