Amid reports of destruction in Bengkulu, Sumatra, police chief Budi told local radio there had been scenes of panic as people tried to save themselves.
The quake caused a blackout, Bengkulu resident Edi Santoni, 38, told the Reuters news agency.
" I rushed out of my house," he said. "I don't know if there's any damage because it's dark."
"Everyone is running out of their houses in every direction," Wati Said told the Associated Press by mobile phone from Bengkulu.
"We think our neighbourhood is high enough. God willing, if the water comes, it will not touch us here. We are all afraid."
'Hands still shaking'
The quake was felt in the Indonesian capital, Jakarta.
"It was much, much stronger than the one we had earlier in the year"
"It happened twice," he told the BBC News website.
"We took time to understand that it was a earthquake. Then we started running to the staircase."
When he and the others reached the lobby, they found the building had not been damaged and returned to their desks.
" It was a horrible experience to me - still my hands are shaking," he writes in his e-mail.
'Stronger than before'
BBC News website readers as far away as Singapore and Malaysia also registered tremors.
"I was working on my laptop and felt my block shake," Mohamed Faiz Nagutha writes from Singapore.
"My uncle soon called to say they felt it too. Some office buildings in the city were apparently evacuated."
Peter Sinniah in Petaling Jaya, Malaysia, writes that the tremors lasted nearly two minutes.
"It was much, much stronger than the one we had earlier in the year," he adds.
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