New Zealanders aren't in danger of a tsunami after a 6.5 magnitude earthquake struck Indonesia this morning.

The earthquake hit the main island of Java shortly before 6am New Zealand time on Saturday, the US Geological Survey said.

Buildings in Jakarta were reported shaking and the tremor was measured at a depth of about 90km.

There was no immediate reports of casualties or tsunami threats in Indonesia.

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On Saturday morning a Civil Defence and Emergency Management spokeswoman said there was no threat of a tsunami to New Zealand.

"(The earthquake) is well below our threshold for any tsunami," she said. "There's no danger."

There had been no alerts from anywhere else in the Pacific either, she said.

GeoNet duty seismologist Matt Gerstenberger said there "shouldn't be any" effect on New Zealand and if there was any, such as high waves, it would be "very minimal".

Because of the depth of the earthquake tsunami was unlikely, he said.

The Ministry of Foreign Affairs and Trade has been contacted for comment.