JAKARTA: Indonesia's capital Jakarta reopened 600 of its schools on Monday as coronavirus restrictions eased, though a teacher federation urged caution and warned of clusters in classrooms caused by the highly transmissible Delta variant.

Jakarta's infection rate has dropped, authorities said, from a peak last month that saw Indonesia become Asia's coronavirus epicentre, with more than 4 million cases and 131,000 fatalities overall.

Jakarta Governor Anies Baswedan said 610 of 10,000 schools deemed safe had opened at 50% capacity in a resumption of a trial that started in April.

"The conditions of the COVID-19 pandemic are much more under control," he said on Instagram.

Vaccinations are not mandatory for at-school learning, Anies has said, adding that 91% of children aged 12-18 and 85% of educators have been fully inoculated. Nearly 70% of Jakarta's 10 million population have been vaccinated.

Zhafira Tsamara Ufaira Azza, 6, was excited to be back at school, where students will rotate with one day per week in class and the rest online at home.

"I got to meet my friends and teachers," she said.

Mother Endang Sugiarti, 35, said she was still worried about the Delta variant.

"But for my daughter's progress and education, I dared to try it first," she said.

Education Minister Nadiem Makarim last week called for school reopening to be accelerated to try to recover lost ground.

"There's a decrease in study targets, lots of children quit school, especially girls in some regions," he said.

"There's a learning loss with permanent impacts."

But Heru Purnomo, of The Federation of Indonesian Teachers Associations, said broadening the reopening could be risky.

According to official data, about 1% of Indonesian coronavirus deaths and 13% of its cases have been minors.

"It could create new clusters...it could add to the death of children," he told Reuters.