(Adds tsunami danger has passed, witness comment)
By Alison Bevege and Jane Wardell
SYDNEY, March 30 (Reuters) - A magnitude 6.9 earthquake struck off the southern coast of Papua New Guinea's New Britain island on Friday, initially triggering a tsunami warning for surrounding coastlines, but there were no immediate reports of casualties or damage.
The shallow quake struck close to the coast, around 100 miles (162 km) southwest of Rabaul, a much more remote region than the country's mountainous mainland highlands where a magnitude 7.5 tremor struck on Feb. 26, killing 100 people.
The Pacific Tsunami Warning Centre (PTWC) issued a threat warning for the country's coastline located within 300 km of the quake's epicentre, but later advised that the threat had passed.
Dellie Minding, a receptionist at the Rabaul Hotel in the east of New Britain, around 20 minutes from the coast, told Reuters that the earthquake was felt, with many guests running outside, but there was no damage.
At the Rapopo Plantation Resort on the coast, receptionist May Dovon said she had not heard of any casualties or damage.
"We felt the earthquake, everything was moving so we went out of the building," Dovon told Reuters. "Nothing was damaged."
Australian authorities said there was no threat to the Australian coastline from the quake, which was initially reported as a magnitude 7.2.
Quakes are common in Papua New Guinea, which sits on the Pacific's "Ring of Fire", a hotspot for seismic activity due to friction between tectonic plates. Rabaul lies in the shadow of Mount Tavurvur, an active volcano that destroyed the town in 1994 during a severe eruption.
The latest quake came as Papua New Guinea struggles to get aid to survivors of the Feb. 26 quake, which flattened whole villages and spoiled water supplies on the country's main island.
The impoverished country is also missing its largest revenue earner since the quake forced a shutdown of Exxon Mobil Corp's liquefied natural gas (LNG) project, which has annual sales of $3 billion at current LNG prices. The company is still assessing quake damage at its facilities. (Reporting by Jane Wardell and Alison Bevege in SYDNEY. Additional reporting Sandra Maler in Washington Editing by James Dalgleish, Tom Brown, Toni Reinhold)