Sydney - Despite security being so tight at Jakarta's JW Marriott Hotel - guards, metal detectors, even Rottweiler dogs - Australian guest Lesley Harbon had no doubt a bomb had gone off 11 floors below - where her husband, Paul, was having breakfast.

"It doesn't sound like anything else you've ever heard," the Sydney University academic said. "You couldn't mistake it."

Paul Harbon had been impressed with security when checking in the night before.

"They checked underneath the taxi, we had to go through metal detectors, there were six guards and a Rottweiler dog," he told The German Press Agency dpa in a phone call from their new Jakarta hotel.

He also had no doubt about what he had heard when having that last cup of coffee and Danish pastry while his wife was 11 floors above reading notes ready for a business meeting.

"It was a big dull thud," he recalled. "All the walls on one side had big cracks and the awnings were down. For the next half hour people were being dragged out. It wasn't the devastation that you could see in, say, the Bali blasts."

He had an easier time evacuating than his wife.

"I ended up in the bottom of the building, there was flood water everywhere and there were no lights. I just screamed and screamed until someone came to get me out," she said.

Both praised the Marriott staff, saying they were calm and busied themselves accounting for all the guests.

Peter Toomey, an Australian businessman staying at the same hotel, said the presumed terrorist attack would not deter him from regular visits to Jakarta.

"It's just a shame for Indonesia that this has happened," he said. "It's part of life. Perhaps I'll be somewhat more careful but I wouldn't be deterred. That's it really." (dpa)