HONOLULU -- A day after rumors of a looming earthquake and tsunami scared people statewide, officials are trying to figure out how the false story got started.

Officials want to know if it was innocent but misguided gossip or an organized hoax.

Civil Defense officials said that Sunday's rumors were the worst, fastest-spreading rumors they have seen.

The rumors caused people to stock up on water and essential foods, fill up their cars with gas and even evacuate from some low-lying areas.

Hawaii state Civil Defense took at least 500 calls from people on Sunday night, asking about whether an earthquake was going to hit.

The day after the hoax officials said they are not sure where the rumor started.

Vice Director of state Civil Defense Ed Teixeira said the first callers said they heard from people on the mainland that an earthquake was predicted for the islands. Later, people called saying they had heard the rumor from a friend of a friend or relative that worked at Civil Defense offices, the National Weather Service or the Pacific Tsunami Warning Center.

Teixeira had the FBI, state Attorney General's office and Honolulu Police Department listen in on a briefing about the rumors. So far, there is no formal criminal investigation.

"So, I wanted law enforcement to hear it, because if it was deliberately set, we can't sit still," Teixeira said.

At least 250 calls came into the Pacific Tsunami Warning Center, where Brian Shiro was on duty.

"In general, it was that we're predicting that something was going to happen, which is just impossible. We cannot predict when an earthquake or tsunami is going to happen before it happens," Shiro said.

Elisha Hirakawa of Hawaii Kai got a warning call from friends and stocked up on emergency supplies, even moving breakables from shelves at home.

"In my mind, I'm thinking, 'OK, well, maybe there's somebody who knows something, and maybe it's a cover up, and there's all these small things that are happening that they can chart that we don't know about,'" she said.

Big Island Mayor Harry Kim said he thinks people believed the rumors because they were already on edge from the earthquakes and small tsunami surges in recent weeks. Plus, concern over the destruction from Hurricane Katrina in the south and the deadly tsunami in Asia in early 2005.

"I got very, very concerned because of the fear that it created," Kim said.

The county mistakenly waited until 8 p.m. to call radio stations to quell the quake rumors, he said.

"If we had gotten on it earlier, I think, obviously we could have stopped them from spreading so far and fast on this island, and I hope next time we'll learn from this," Kim said.

Word began circulating as early as 7 a.m. or 8 a.m. on Sunday. Some people heard about the quake rumor at early church services, Kim said.

As word traveled throughout the day, people eventually began deluging news organizations, police departments and civil defense offices. The calls reached a peak between 6 p.m. and 8 p.m.