Mobile phone calls in Sydney's CBD will be blocked by a sophisticated counter-terrorism measure to prevent bomb attacks during US President George W Bush's September APEC visit.

The president's motorcade will be shadowed by a helicopter equipped with signal-jamming equipment, News Limited newspapers report.

Terrorists have used mobile phones to detonate remote-controlled bombs in Iraq and in the second Bali bomb attacks.

It is expected mobile phone calls will drop out in an area the size of a football field as the helicopter passes overhead.

The technology was first used by the US president when Mr Bush attended the APEC summit in Pusan, South Korea, in 2005.(from brisbanetimes.com.au)