Arizona police split on new immigration law

However what they were preparing was distinctly different in each county.

Maricopa County Sheriff Joe Arpaio is preparing a vast outdoor jail, determined to round up illegal immigrants to fill it.

He plans to send up to 200 deputies and volunteers out, looking for traffic violators, people wanted on criminal warrants and others.

He's used that tactic before to arrest dozens of people.

Elsewhere in the state, police said they didn't expect any dramatic events.

And some police chiefs are publicly dismissing the law as virtually unworkable. "Am I going to sit here and say I think every officer has a clear understanding of the law when they leave training?" Tucson Police Chief Roberto Villasenor asked.

"No, because I think the law is poorly constructed."

Protests are planned throughout Phoenix. The law is creating a volatile mix of police, illegal immigrants and thousands of activists, many planning to turn up without identification as a show of solidarity.

At least one group plans to block access to federal offices, daring officers to ask them their immigration status.

"Our message for that day is Don't Comply, Don't Buy," said activist Liz Hourican, whose group, CodePink, plans to blockade the immigration offices in central Phoenix.

US District Judge Susan Bolton is deciding whether to step in and block the law.

It requires officers enforcing other laws to check a person's immigration status if they suspect that they are in the country illegally.

Police training videos say that signs that might indicate a person is an illegal immigrant are speaking poor English, looking nervous or travelling in an overcrowded vehicle.

A dawn march from the state Capitol is planned, followed by a prayer service, a rally outside Sheriff Arpaio's office and later in the afternoon a concert outside a Maricopa County jail, according to the Los Angeles-based National Day Labourer Organising Network (NDLON).

The protesters from Arizona and elsewhere plan to show up without identification and hold peaceful rallies.

"It's defiance, to see if they want to come and arrest those people," said NDLON executive director Pablo Alvarado. "We dare them to come and ask."