The Teenage Mutant Ninja Turtles and Guardians Of The Galaxy have fought off a challenge from Sylvester Stallone and his all-star Expendables to stay atop an action-packed box office.

The Expendables 3 underperformed in its opening weekend, picking up $10 million less than expected to debut behind the Turtles and Guardians at number four.

The new sequel opened with $16.2 million - less than half the figure the first movie debuted with in August, 2010 - and was beaten to a top three spot by comedy Let's Be Cops.

Meryl Streep and Jeff Bridges' new movie adaptation of Lois Lowry's beloved book The Giver opened at five.