United Nations, Jan 16 : UN Secretary-General Antonio Guterres has expressed deep concerns after reports of a tsunami and ash affecting Tonga following the eruption of an undersea volcano near the Pacific nation. Tsunami warnings have been issued in countries such as Australia, New Zealand, Japan and the US, reports Xinhua news agency. "The UN offices in the Pacific are closely monitoring the situation and are on standby to provide support if requested. The Secretary-General is grateful to countries that have already offered their support," Farhan Haq, deputy spokesman for Guterres, said in a statement. According to the Tonga Geological Services, a massive underwater volcano erupted on Friday with plumes reaching more than 19 km above sea level. A cloud of ash and steam reached about 241 km across, an event captured by satellite images that have been shared by various meteorological agencies. There was no immediate report of injuries or damage due to the nation's current lack of connectivity. /IANS