NEW YORK (AFP) - As millions of Americans around New York and New Jersey began their commutes Monday, their cellphones abruptly alerted them to a manhunt for a suspect in weekend bombings in the area.

"WANTED: Ahmad Khan Rahami, 28-yr-old male. See media for pic. Call 9-1-1 if seen." It was the first time the national Wireless Emergency Alert system was used in the search for a criminal or terror suspect, according to media reports.

The system, managed by the Federal Emergency Management Agency, is usually used to warn about dangerous weather or missing children. Monday's use amounted effectively to an "electronic wanted poster," as the New York Times put it.

Cellphone users in a geographically targeted area automatically receive text message-like notifications about public safety emergencies or threats, accompanied by loud buzzes or phone vibration. Cell phone users may choose to not receive the alerts, or can shut off the audible signal.

Extreme weather and other threatening emergencies like forest fires or chemical spills; kidnapped children ("Amber Alerts"); "Presidential Alerts" during a national emergency.

National, state or local agencies; the National Weather Service. In the case of Amber Alerts, the National Centre for Missing and Exploited Children in conjunction with local law enforcement.

The system operates through cell towers in the alert zone. That means a Californian visiting New York on Monday would have received the Rahami alert.

Wireless carrier participation is widespread but voluntary. Major wireless companies, including AT&T and Verizon, distributed the Rahami alert Monday. There is no charge for receiving the alert.

Cellphone users can opt out of danger alerts and Amber Alerts. However, they cannot block Presidential Alerts.