Australia will be extending a US$50,000 cash assistance to the Tonga government to help survivors of the category five storm Cyclone Ian that lashed on the Ha'apai group of islands over the weekend.

Julie Bishop, federal Foreign Minister, said on Tuesday the amount will be an initial one that can be immediately used to purchase emergency and relief items such as blankets, water containers, tarpaulins, kitchen sets and hygiene kits.

New Zealand has likewise pledged US$50,000 for the relief efforts in Tonga.

Radio Australia reported telecoms companies have restored mobile phone services in the Ha'apai islands.

"We've established communications on both telephone companies, electricity should be on at the hospital today, however, we have a standby generator," Samiu Vaipulu, Tonga's deputy prime minister, said.

"Water is now running, so we're in much better than as of Sunday." However, 88 per cent of the 4,500 residents still remain homeless.

"I've been in cyclones... but this one here is the first one that I've seen this much damage in Ha'apai," he said. Some of the displaced residents have been allowed to move out of emergency shelters.

"The tents will give them the option to go back, to start going back to their respective places," Leveni Aho, Tonga's director of emergencies, told Radio Australia. "Although they have lost a house, they can at least start go back and put their belongings, or find their belongings."

Around 2,000 people are currently housed in 11 evacuation centres across the region, according to the United Nations Office for the Coordination of Humanitarian Affairs.

Gusts from Cyclone Ian reached 300 kilometres per hour when it struck into the northern Tongan islands early Saturday, local time.