A tsunami watch was issued for countries across the Indian Ocean on Wednesday after a large earthquake hit waters off Indonesia, sending residents pouring from their homes in panic. Tremors were felt in several cities in India where a tsunami warning has been issued for the Andaman and Nicobar Islands. The US Geological Survey said the 8.7-magnitude quake was centred 20 miles (33 kilometres) beneath the ocean floor around 269 miles (434 kilometers) from Aceh's provincial capital. The Pacific Tsunami Warning Centre in Hawaii said a tsunami watch was in effect for Indonesia, India, Sri Lanka, Australia, Myanmar, Thailand, the Maldives and other Indian Ocean islands, Malaysia, Pakistan, Somalia, Oman, Iran, Bangladesh, Kenya, South Africa and Singapore. A tsunami watch means there is the potential for a tsunami, not that one is imminent. "Earthquakes of this size have the potential to generate a widespread destructive tsunami that can affect coastlines across the entire Indian Ocean basin," the US Pacific Tsunami Warning Centre said. The US Geological Survey said an 8.7-magnitude earthquake struck off the coast of Sumatra at 1408 IST at a depth of 33 kilometers. USGS had initially reported it as an 8.9-magnitude quake. The tsunami warning center said it had not yet ascertained whether a tidal wave had been generated but that one was likely given the strength of the temblor, and advised local authorities to take "appropriate action." Said, an official at Indonesia's Meteorology and Geophysics Agency who goes by only one name, said a tsunami warning has been issued for cities all along the coast of Sumatra island. The tremor was felt in Singapore, Thailand, Bangladesh, Malaysia and India. High-rise apartments and offices on Malaysia's west coast shook for at least a minute. People in Banda Aceh screamed ''God is great!'' as they jumped into cars and the backs of motorcycles, clogging streets as they fled to high ground. Indonesia straddles a series of fault lines that makes the vast island nation prone to volcanic and seismic activity. A giant 9.1-magnitude quake off the country on December 26, 2004, triggered a tsunami in the Indian Ocean that killed 230,000 people, nearly three quarter of them in Aceh.