Major quake occurred with epicentre in Costa Rica in Central America (south of Mexico) at 12:42am AEST. Magnitude detected by USGS was 7.6 (revised down from the preliminary 7.9) with depth of 46km.
The Joint Australian Tsunami Warning Centre has issued a No Threat bulletin for Australia at time of writing this.
However, for areas close to the quake, the Pacific Tsunami Warning Centre has them currently under a tsunami warning as follows:
TSUNAMI BULLETIN NUMBER 001PACIFIC TSUNAMI WARNING CENTER/NOAA/NWSISSUED AT 1450Z 05 SEP 2012
THIS BULLETIN APPLIES TO AREAS WITHIN AND BORDERING THE PACIFIC OCEAN AND ADJACENT SEAS...EXCEPT ALASKA...BRITISH COLUMBIA...WASHINGTON...OREGON AND CALIFORNIA. ... A TSUNAMI WARNING AND WATCH ARE IN EFFECT ... A TSUNAMI WARNING IS IN EFFECT FOR COSTA RICA / PANAMA / NICARAGUA / EL SALVADOR / HONDURAS /MEXICO / COLOMBIA / ECUADOR / GUATEMALA / PERU
A TSUNAMI WATCH IS IN EFFECT FOR CHILE
It's unknown yet whether or not tsunami was caused but will know soon when readings from tidal gauges and the DART tsunami detection buoys come in. Here's a map showing possible max tsunami wave heights (in metres) generated by JRC modeling: