'EWA BEACH — Several South Pacific island nations were inadvertently left off a list of areas predicted to be hit by a tsunami after a powerful underwater earthquake that struck this week near Tonga.

The first alert issued by the Pacific Tsunami Warning Center, based in 'Ewa Beach, warned that an earthquake occurred near Tonga and that a tsunami warning was in effect for just Fiji and New Zealand.

But Tonga — the country closest to the epicenter, where the danger of a giant wave was greatest — and several other nearby nations were not given tsunami "warning" or "watch" status on the initial alert that was issued at 5:42 a.m. Hawai'i time Wednesday (4:42 a.m. Thursday in Tonga).

"That was a foul-up," the center's acting director Gerard Fryer said. "That was a mistake on our part. We had a processing error."

Tongan authorities earlier said that they didn't receive the tsunami alerts.

There were no reports of injuries from the magnitude-7.9 temblor, which struck about 95 miles south of Neiafu, Tonga, and 1,340 miles north-northeast of Auckland, New Zealand. Authorities lifted the tsunami warnings within two hours.

A second bulletin issued at 6:31 a.m. Hawai'i time, 49 minutes after the first alert, correctly included Tonga, Niue, American Samoa, Samoa and Wallis-Futuna as places also under the tsunami warning.

By that time, it would have been too late if a destructive tsunami had been generated.

Only Wallis-Futuna and Fiji had estimated tsunami wave arrival times after the second alert was issued. Tonga's expected tsunami arrival time was 5:51 a.m. Hawai'i time and Niue was six minutes later — well after the second alert was issued.

Fryer said a glitch in the center's computer database caused the problem, and a staffer failed to catch the omission in the rush to get out alerts.

"They were so eager to get the message out that all they did was to check the earthquake had the right parameters," he said. "They didn't check to see who was on the warning."

Fryer, who was not on duty when the earthquake occurred, said he believes the second, corrected message could have gone out at least 20 minutes earlier.

The center has made corrections and improvements since the tsunami scare, including the implementation of an automatic second check built into the software.

"We're still trying to figure what went wrong, but that error will not happen again," he said.

The countries still received the center's bulletins, even if they were not listed as being under a tsunami warning or watch in the initial alert.

All except for Tonga.

The Pacific Tsunami Warning Center earlier said Tonga — a 170-island archipelago about halfway between Australia and Tahiti — failed to receive the warnings because of a power failure. Officials at the center said they didn't know the nature of the power failure.

Fryer said another messaging scheme may be necessary for Tonga, which has a population of about 108,000 and isn't among the 26 nations in the Pacific Tsunami Warning System.

Mali'u Takai, deputy director of Tonga's National Disaster Office, said the failure to get a warning could have proved deadly, as the epicenter of the earthquake was just 95 miles south of the Tongan island of Neiafu.

"Nobody got a warning through the emergency satellite system in our meteorological office," Takai said. "Judging by the location of the epicenter, we would have been caught out without any warning at all because of the system's malfunction."

A pair of aftershocks rattled Tonga today but caused no damage or injuries. The magnitude 6.0 and magnitude 5.4 aftershocks hit the same region of Tonga, the U.S. Geological Survey reported, but no tsunami warnings were issued.

Though a major tsunami failed to materialize after Thursday's quake, the communications failure raised troubling questions about the effectiveness of such alerts, which have come under global scrutiny since an earthquake-driven tsunami in the Indian Ocean nearly 18 months ago left at least 216,000 people dead or missing.

Fryer said the omission of the countries from the warning was the biggest problem identified in the real-life test.

"Nobody went home yesterday until after we had beaten all of this to death," he said.

The communications failure in Tonga lends greater urgency to a test of alert systems in 23 countries on both sides of the earthquake-prone Pacific. The test is scheduled to take place in two weeks.

The center in 'Ewa Beach, which falls under the National Oceanic and Atmospheric Administration, was criticized for not reporting more aggressively on the 2004 tsunami.

On Dec. 26, 2004, the most powerful earthquake in four decades — a magnitude 9.0 — ripped apart the Indian Ocean floor off Indonesia's Sumatra island, displacing millions of tons of water and spawning giant waves that sped off in all directions.