"The entire population of the coastal zones needs to move to higher ground. The US Department of Defence has discovered a possible tsunami", Bukele wrote on Twitter.
Earlier in the day, the US Embassy in El Salvador said that a US military aircraft spotted a potential tsunami 600 kilometers (370 miles) off the coast of El Salvador and Nicaragua, and urged its personnel to leave the dangerous areas.
In May, a 6.6-magnitude earthquake occured near the coast of El Salvador at a depth of 65 kilometres.