A tsunami alert for New Zealand after a massive earthquake near Tonga has been cancelled.

The 7.9 magnitude quake saw New Zealand's Civil Defence go on to alert and start monitoring the potential risk of a tsunami hitting New Zealand.

The quake, which struck at 7.17am New Zealand time, caused damage and panic around Tonga but no major infrastructure damage has been reported.

Initial reports suggested there was a risk to New Zealand prompting the Ministry of Civil Defence and Emergency Management to issue an alert at 8.10am.

"It is possible that there is a tsunami risk to New Zealand from an earthquake that occurred in Tonga Islands Region today at 07:18 NZDT. The Ministry of Civil Defence & Emergency Management is continuing to monitor the situation," the statement said.

The Ministry based that warning on information received about the earthquake from the Pacific Tsunami Warning Centre (PTWC) in Hawaii and GNS Science in New Zealand.

International media reports suggest a small tsunami was generated by the quake but the Pacific Tsunami Warning Center has since lowered and cancelled its warning.

Earthquake details:
Location: Tonga Islands Region
Time and date: 1818Z 19 March 2009
NZ Origin time: 0718 NZDT 20 March 2009
Co-ordinates: 23.0 South 174.8 West
Depth: 48 Km
Magnitude: 7.7 (Magnitude is provisional and may be adjusted as more seismic data becomes available)