Tonga's National Emergency Management Office said it was still calm in the capital but that was expected to change soon.
A state of emergency has been declared.
"On its projected path, Severe TC Gita is anticipated to affect southern Tonga and enter Fiji waters on Monday night (tonight) and pass south of Ono-i-Lau as a Category 4 system on Tuesday night (tomorrow)".
Forecasts are now about half and half on whether the remnant of the storm will eventually make landfall in New Zealand next week. About 300 people had evacuated but were now returning to their homes, Butler said.
The tropical cyclone has been upgraded to moderate to high with wind speeds of up to 86k/h expected.
Many models are predicting it would hit New Zealand, but not until the middle of next week.
Neighbouring countries American Samoa and Samoa suffered significant damage over the weekend with Samoa declaring a state of emergency.
Tens of thousands of people on Tonga's main island are preparing for the worst as Cyclone Gita bears down with category four force.
Gita will pass near Niue on Saturday and then pass just to the south of Tonga.
Acting Prime Minister Semisi Sika announced the state of emergency at 10am, saying this was due to the destructive force winds and expected sea level rise brought by Gita.
Tonga was braced Sunday for "very destructive winds" as Cyclone Gita took aim at the Pacific island nation a day after it wreaked havoc in Samoa.
The Metservice also warned of huge coastal swells and flooding of low-lying areas.
"It is now moving west towards the southern islands in Tonga, and has the potential to strengthen to a category 5 with winds in the centre reaching 200km/h".
He has stressed that people to listen to weather bulletins, remain alert and be prepared at all times adding that should the stronger winds expand the Weather Office will adjust the projected tracks as the information comes on hand.
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