LOS ANGELES - BEN Stiller's 'Night at the Museum' sequel crushed the fourth installment of the 'Terminator' franchise in a battle for North American box office supremacy between two special-effects extravaganzas.

According to studio estimates issued on Monday, 'Night at the Museum: Battle of the Smithsonian' earned US$70 million (S$105 million) during the four days beginning on Friday, outperforming the expectations of its distributor, 20th Century Fox.

On the other hand, Warner Bros' 'Terminator Salvation' - the first in the series without Arnold Schwarzenegger - made its debut at No 2 with a disappointing US$54 million.

'Star Trek' slipped one place to No 3 with $29.4 million in its third weekend. Reigning champ 'Angels & Demons' fell to No. 4 with $27.7 million in its second weekend, although the Tom Hanks Vatican thriller remained the top choice internationally.

Big studio movies rarely open against each other during the lucrative summer period in order to avoid cannibalisation.

But in this case families made up almost half of the audience for 'Night at the Museum' while men accounted for 70 per cent of the audience for 'Terminator.'

Fox, a unit of News Corp said it would have been happy with a four-day opening above US$60 million. The film cost about US$125 million to make.

The first movie, 'Night at the Museum,' earned US$30 million during its first three days just before Christmas 2006, and went on to make US$250 million.

The previous 'Terminator' film, 'Terminator 3: Rise of the Machines' finished with US$150 million in 2003, an indication of the new film's underdog status in the weekend derby. -- REUTERS