Image caption Gravity is about an engineer and an astronaut trying to survive being left adrift in space

Space film Gravity, starring Sandra Bullock and George Clooney, has shot straight to the top of the US box office in its opening weekend.

According to early estimates, the movie took $55.55m (£34.62m) over the weekend, making it the biggest October opening since records began.

The figure also ensured it was the biggest opening for a film starring Bullock or Clooney.

The film, set almost entirely in space, is directed by Alfonso Cuaron.

Bullock and Clooney play an astronaut and a medical engineer who work together to survive after an accident leaves them adrift in space.

Last week's number one, Cloudy with a Chance of Meatballs 2, dropped into second slot with $21.5m (£13.4m).

Based on a children's book, the first film - Cloudy With A Chance Of Meatballs - was a breakout hit for Sony Animation in 2009.

The follow-up is an original story, in which inventor Flint Lockwood must save the day after one of his inventions malfunctions, creating food-animal creatures, or animals made of food, that overtake the region of Swallow Falls.

Adult drama

Runner Runner, starring Oscar-winner Ben Affleck and pop star and actor Justin Timberlake, opened in third place, taking just $7.6m (£4.7m).

The crime thriller follows Timberlake as a graduate student who goes to Costa Rica to confront an online gambling tycoon played by Affleck, who swindles him.

Former number one Prisoners, starring Jake Gyllenhaal and Hugh Jackman, slipped from second place to fourth.

Formula One movie Rush, which depicts the rivalry between James Hunt and Niki Lauda, took fifth spot.

Joseph Gordon-Levitt's directorial debut, Don Jon, about a porn addict looking for love, was next in sixth place.

"The adult drama is back, and fall is the season for the adult drama," said Paul Dergarabedian, senior media analyst for box-office tracker Rentrak.

"This is when you get your more challenging films, some of the more esoteric fare."