Millions of Asians have been reliving the panic of the December tsunami, after feeling or hearing about the latest earthquake in Sumatra.
Many people fled Banda Aceh in the middle of the night
Across the Indian Ocean region, coastal residents fled to higher ground.
But amid the panic, the region showed it was much better prepared for such an emergency than it was for the quake three months ago.
Although the regional tsunami early warning system agreed after that disaster has yet to be put in place, officials were quick to spread the word to Sri Lanka, the Maldives, Thailand and beyond.
Information about Monday's earthquake off the coast of Indonesia was immediately relayed across the region by the Pacific Tsunami Warning Centre in Hawaii.
TV and radio, loudspeakers and even church bells were then used to spread the message around coastal areas, in case the tremor triggered another tsunami.
Fleeing Banda Aceh
In Banda Aceh, one of the cities worst hit by the last disaster, Monday's earthquake triggered mass panic.
Electricity was cut off in most areas of the city, plunging it into darkness, and thousands of people reportedly fled for higher ground, ignoring official pleas for calm.
"It was horrible, the only thing on my mind was how to get out of the house immediately and save my 3-and-a-half month baby girl," 27-year-old Marlina told the Associated Press.
"I felt the earthquake and I just jumped on my motorbike," said Wayu, who lost his parents and five other family members in the disaster three months ago.
"As I drove, I was thinking of those relatives I lost."
The BBC correspondent in the area, Rachel Harvey, says that people in Aceh are now becoming almost accustomed to tremors and aftershocks, but that this one was much more prolonged and sparked fears of a tsunami.
Sri Lankans were quick to move to higher ground
Locals watched the sea carefully, and when it did not retreat or "boil" like it did before, they were relieved and returned to their homes, she said.
Compared to the disaster three months ago, news emerged relatively quickly from the worst-hit areas.
In Sri Lanka, for example, the military had been informed and had prepared all their local officers just half an hour after the quake.
Much of the nation's east coast then awoke to the sound of warning sirens. Church bells rang to alert people to the danger, while police toured districts to urge people to move inland.
In Thailand, too, a local warning system was utilised effectively. An alert was sounded across coastal areas about 35 minutes after news of the quake.
Thai Prime Minister Thaksin Shinawatra praised the system, saying: "We managed to alert people in enough time for them to seek safety."
Thailand's meteorology department said Monday's alert was an "effective rehearsal".
People raced away from the famous Patong beach, on the tourist island of Phuket, creating large traffic jams on main roads away from the coast.
Hundreds gathered at the Phuket town hall until the all-clear was given.
George Pararas-Carayannis, the retired director of the International Tsunami Centre in Hawaii, said it would be several months before the main regional warning system would be in place.
An incident such as Monday's earthquake in Indonesia proves just how vitally - and rapidly - such a system is needed.