SYDNEY/WELLINGTON, Jan 17 (Reuters) - Australia and New Zealand dispatched surveillance flights on Monday to assess the damage in Tonga, isolated from the rest of the world due to the eruption of an underwater volcano that triggered a tsunami and blanketed the Pacific island with ash. Australian Prime Minister Scott Morrison pledged to provide support for Tonga as early as possible but said the volcano ash had hampered relief efforts. "There"s been a lot of challenges there with the ash cloud and the disruption to communications and so we are working together to get as much support to Tonga as we possibly can," Morrison told radio station 2GB on Monday. Australia"s Minister for the Pacific Zed Seselja said initial reports suggested no mass casualties and that the airport "appears to be in relatively good condition" but there were "significant damage" to roads and bridges. Seselja said Australia was liaising with the United States, New Zealand, France and other countries to coordinate responses. An underwater volcano off Tonga erupted on Saturday, triggering a tsunami on the shores of Tonga and cutting off phone and internet lines for the entire island. There are no official reports of injuries or deaths in Tonga as yet but communications are still limited and outlying costal areas remain cut off. Satellite images show some of the outlying islands are submerged in water. A U.K. woman has reportedly gone missing after she was washed away, media reports said. Angela Glover and her husband James, who own the Happy Sailor Tattoo in Nuku"alofa, had gone to get their dogs when the wave hit. James managed to hold onto a tree but his wife, who also runs a dog rescue on the island, and their dogs were washed away, New Zealand state broadcaster TVNZ reported. Several social media posts from family and friends said she has still not been found. New Zealand"s Prime Minister Jacinda Ardern said on Sunday that the tsunami had a significant impact on infrastructure. Red Cross said it was mobilising its regional network to respond to what it called the worst volcanic eruptions the Pacific has experienced in decades. “Red Cross currently has enough relief supplies in the country to support 1,200 households with essential items such as tarpaulins, blankets, kitchen sets, shelter tool kits and hygiene kits,” said Katie Greenwood, IFRC’s Pacific Head of Delegation. The agency said there were concerns that communities may not have access to safe drinking water as a result of saltwater inundation caused by the tsunami waves and ashfall. Shelter is also a concern, particularly for those communities near the coastline, it added. United Nations Secretary General Antonio Guterres said on Twitter that the UN offices in the Pacific are on standby to provide support. MASSIVE BLAST The Hunga-Tonga-Hunga-Ha"apai volcano has erupted regularly over the past few decades but the impact of Saturday"s eruption was felt was far away as Fiji, New Zealand, the United States and Japan. Two people drowned off a beach in Northern Peru due to high waves caused by the tsunami. About 26 hours since the eruption, nations thousands of kilometres to the west have volcanic ash clouds over them, New Zealand forecaster WeatherWatch said in a statement. Fiji, Vanuatu and New Caledonia are affected and the ash cloud is expected to fan out towards eastern Australia on Monday, it said. Early data suggests the volcanic eruption was the biggest blast since Mount Pinatubo in the Philippines 30 years ago, New Zealand-based volcanologist Shane Cronin told Radio New Zealand. "This is an eruption best witnessed from space," Cronin said. "The large and explosive lateral spread of the eruption suggests that it was probably the biggest one since about the 1991 eruption of Pinatubo," Cronin said.