When the earth shook under their feet on Wednesday, students and staff at Jeumpa Puteh high school coolly continued with lessons, assuming it was just another tremor in Indonesia's quake-prone Aceh province.

"But the shaking became stronger and stronger," said 15-year-old student Zikra Latasha of Wednesday's 8.6 magnitude undersea quake off Sumatra.

"For five minutes, the trees swayed, the cars jerked back and forth and the glass windows rattled. We knew this was a big one and that we must get out."

They knew the drill by heart: that when an earthquake strikes they should never panic, and concentrate on moving to an open area or higher ground.

From the compound, the school headmaster bellowed into a bullhorn, ordering students to follow the red-and-blue arrows painted on the walls, guiding them to an open field more than a half mile away.

Chanting "Subhanallah" (Glory to God), they grabbed their bags and trooped out of their classrooms as they came to realise that a giant quake -- the biggest since the 2004 Indian Ocean tsunami that killed 170,000 in the province alone -- had just struck.

Wednesday's quake was felt as far afield as Thailand while India, Indonesia, Kenya, Malaysia, Reunion Island, Sri Lanka and Myanmar also issued alerts or evacuation orders.

It was followed by another powerful aftershock, triggering another Indian Ocean-wide tsunami alert, but the threat eventually subsided and damage was minimal.

"Nobody shoved and pushed -- we did what we had learned during disaster drills," said Rumiana, a 52-year-old maths teacher who goes by one name.

"But the stress was too much to handle -- students were crying, calling out for their parents, clinging to my dress. A few students had difficulty breathing and one even fainted," she added.

Her colleague, chemistry teacher Zahratus Safara, 50, said they held hands and huddled together to stay calm.

In the more than seven years since the 2004 tsunami, which devastated the province, Indonesia has invested heavily in an early warning system, quake-resistant buildings and disaster mitigation measures.

Jeumpa Puteh is one of the nearly 30 disaster-prepared schools in the province that has undergone disaster management training under a program by Aceh's Tsunami Disaster Mitigation Research Centre (TDMRC).

School staff and students have received first aid lessons and regularly conduct mock drills to test their disaster preparedness.

In the Blang Oi elementary school, where only six teachers and students survived the "big tsunami" of 2004, staying safe is a simple exercise.

"If there's a quake cover your head/ If there's a quake go under the desk/ If there's a quake avoid windows / If there's a quake run to an open space", the 12-year-olds merrily sang during a recent quake-simulation drill.

When the alarm sounded, they covered their heads with books and schoolbags and briskly walked out of their classrooms in single file.

After Wednesday's quakes, in which five people died of heart attack and shock, Acehnese expressed greater confidence in coping with such disasters than they did eight years ago.

TDMRC coordinator Faisal Ilyas said Wednesday's quakes proved to be a key test of its disaster-preparedness programmes, especially in schools.

"The schools have passed with flying colours. Thousands of teachers and students evacuated according to procedures," he added.

"However, we must not be content and continue to expand our programme to more schools. We must remember this is not the last earthquake," Ilyas said.

Many in the deeply-religious province attribute their safety to divine providence.

"I was afraid that the ground would crack open and swallow me up. I was also afraid everyone would die and leave me on my own," said Koni Armandani, a 15-year-old student.

"We can do all we can but at the end of the day, everything is God's will."