SAIPAN, Northern Mariana Islands -- A magnitude 6.3 earthquake jolted the Northern Marianas and Guam on Wednesday, but seismologists assured terrified residents that the quake wouldn't generate a tsunami.

There were no immediate reports of injuries or major damage on the islands.

The Pacific Tsunami Warning Center, which is located in Hawaii, did not issue a tsunami warning. Despite assurances from local and federal agencies, many terrified residents ran out of buildings and looked out to sea for any sign of a tidal wave.

Rudolfo Pua, head of the emergency management office in the Northern Marianas, said the threshold for issuing a tsunami watch or alert is a magnitude 7.0 quake.

The epicenter of the quake was located about 35 miles west of Rota and 45 miles north of Hagatna, Guam.

Also Wednesday, volcanic haze and ash from Anatahan volcano in the Northern Marianas were continuing to cause respiratory problems for some residents. More than 120 students stayed home from school and at least a dozen people have been treated at hospitals for asthma-related problems in the last two days.

Anatahan, located about 75 miles north of Saipan, began its third recorded eruption in early January. The U.S. Geological Survey said several violent explosions are occurring per minute and ash is spewing up to 15,000 feet.

The smoke and ash, which were previously confined to Saipan and Tinian, has reached Rota and Guam in recent days due to the winds.

Pua said the quake was likely not a result of the eruption at the volcano.