WASHINGTON — America is to build 1,800 watchtowers bristling with high-tech sensors as part of an $8 billion program to secure its borders against undocumented immigrants.

The towers will form the centerpiece of a network to be constructed by the defense and aerospace giant Boeing along the 5,000 miles of border with Mexico and Canada.

Each watchtower will be equipped with a dazzling array of equipment, including cameras that can zoom in on suspicious movements and then transmit live video to border agents with handheld computers. Some of the watchtowers will be on permanent sites and some will be portable.

Unmanned aerial drones launched from the back of border patrol vehicles will also be deployed, as will motion sensors.

“Nothing like this has been done before. Not so much because of the technology that will be used but because of the political atmosphere, geography, topography, and large scope of the project,” Boeing’s Wayne Esser told Bloomberg News.

Boeing has promised to have the system functioning within three years of the contract’s award. This initial contract value is expected to be $80 million.

America has been spending huge sums of money to secure its borders since the September 11 atrocities.

More than a million mainly Hispanic immigrants illegally enter the country every year and now total at least 11 million. American officials fear that terrorists could hide among the human tide.

The government has massively bolstered the border-defense force. The American border patrol now has 12,000 employees and will soon surpass the 12,500 strong Federal Bureau of Investigation to become America’s biggest law enforcement agency. A further 6,000 border patrol agents are currently being hired.