PHOENIX (REUTERS) - An Arizona school district that ignored state safety guidelines and voted to begin in-person learning next week has had to cancel classes after staff said it was unsafe to return and called in sick.

Greater Phoenix's J.O. Combs Unified School District cancelled all instruction for next Monday (Aug 17) due to "insufficient staffing", days after its board disregarded state benchmarks on when students can safely return to classes during the pandemic.

The "sick out" underlined the difficulties in returning to in-person learning in the United States after schools in Tennessee, Georgia, and Alabama closed this week as students and staff were infected with Covid-19 or forced to self-isolate from exposure.

"We have received an overwhelming response from staff indicating that they do not feel safe returning to classrooms with students," J.O. Combs District Superintendent Gregory Wyman said in a statement, adding that he did not know when in-person learning would resume.

Arizona is becoming a battleground in the debate over school reopening, hundreds of parents and students demonstrating on Monday in Phoenix for a return to in-person classes after teachers staged protests calling for a delay until October.

"It was great to see J.O. Combs school district came together and used their collective power," said Ms Kelley Fisher, a Phoenix kindergarten teacher who has led protests by school staff. "I'd love to see a nationwide sick out."

Ms Christina DeRouchey was among Phoenix parents at the Monday rally and led demonstrations in her Deer Valley Unified School District calling for in-person learning to begin next Monday.

When the district delayed the start until mid-October she moved her first-grade son to a charter school where he will start in-person tuition on Monday.

"We just want the choice that is best physically, mentally and most importantly emotionally for our children," said Ms DeRouchey.