South Australia's Country Fire Service (CFS) has issued bushfire emergency warnings for two towns on Kangaroo Island, while an area around Kingscote has gone on a "watch and act" alert.

Key points: Emergency warnings are in place for Vivonne Bay and Parndana

Emergency warnings are in place for Vivonne Bay and Parndana The Defence Force has boosted its presence with the arrival of troop carriers

The Defence Force has boosted its presence with the arrival of troop carriers The weather bureau is forecasting a cooler change, but not until later this evening

The CFS said areas around Vivonne Bay on the south coast and the central town of Parndana were now under direct threat, after fire broke control lines.

"This fire may pose a threat to lives directly in its path," the CFS has told residents.

"Act now. Leave, if the path is clear to a safer place, as it will soon be too dangerous to drive.

"If you cannot leave, identify where you will seek shelter from the bushfire. Heat from the fire will kill you. Do not enter this area as conditions are dangerous."

American River, Nepean Bay, Cygnet River, Emu Bay, Brownlow, Bay of Shoals, Wisanger, Smith Bay and the outskirts of Kingscote are in the watch and act area.

The only designated safer places on Kangaroo Island are Kingscote and Penneshaw.

Fire approaches Vivonne Bay on Kangaroo Island about 5:45pm on Thursday. ( ABC News )

A change is coming through from the west, pushing flames in an easterly direction towards Vivonne Bay and Kingscote.

Winds are expected to later come from the south-west, gusting up to 60 kilometres per hour.

Loading

This will be accompanied by a rainstorm, CFS chief officer Mark Jones said.

"The condition of the fire is such that it is unlikely the fires will be extinguished by the rain and they will continue to burn [on Friday]," he said.

Huge plumes of smoke are billowing above Vivonne Bay, and deputy incident controller Ray Jackson said the Parndana fire remained a threat to a broad area.

"[Residents] are better off, if they have relocated, to stay where they are and remain out of the area," he said.

Mr Jackson said a wind was pushing fires towards Vivonne Bay and along the Cygnet River.

He said Kingscote was not within the warning areas.

On Thursday afternoon billionaire Andrew "Twiggy" Forrest flew into the island, where he owns a property, after earlier donating $70 million for a bushfire recovery package.

Areas under emergency warning on Kangaroo Island shown in red around Vivonne Bay and Parndana. ( CFS )

Vivonne Bay evacuated but two people remain

On Wednesday the CFS took the unprecedented step of evacuating Vivonne Bay, but some residents chose to remain.

"The last couple that were planning on staying, as far as we know, they are currently still there," Mr Jackson said.

Fire burning near Parndana on Kangaroo Island. ( ABC News )

The Ravine fire broke out more than a week ago and has claimed two lives and destroyed more than 50 homes.

Emergency text alerts were earlier issued to residents at Parndana, where the main road has been closed and Australian Defence Force (ADF) helped residents to leave this morning.

"[The] CFS advises that the predicted weather for Kangaroo Island [on Thursday] is highly likely to cause breakouts at multiple points along the fire perimeter," the CFS said in an earlier message.

The Australian Army loaded six armoured personnel carriers onto the Kangaroo Island ferry. ( Supplied: Leon Bignell )

Troops and Army personnel carriers have begun arriving on the island to aid with recovery, boosting the Defence Force's presence after reservists were deployed earlier this week.

"I would say it's unprecedented," local MP Leon Bignell said.

"This is the first time they've deployed on a task like this … when the regular Army turns up, you kind of know that everyone's doing as much as they possibly can."

NASA has also released satellite images of Kangaroo Island, revealing the transformation from wilderness to scorched earth at the western end of the island.

'Beast of a thing' blazing in hot conditions

Temperatures have reached the mid-40s in parts of the state and fire weather warnings for severe fire danger are current for six districts including Kangaroo Island.

"We've got a weak south-westerly coming in during the afternoon but we won't see temperatures drop until the cooler south-westerly change late this evening," Bureau of Meteorology duty forecaster Hannah Marsh said.

"We've got a front coming through which will really increase the south-westerly winds."

Flames near Vivonne Bay on Thursday afternoon. ( ABC News )

Kangaroo Island Mayor Michael Pengilly told ABC Radio Adelaide everyone on the island was "very nervous" ahead of Thursday's conditions.

"It's so frustrating not knowing what this fire's going to do next. It's just a beast of a thing," he said.

A sign at a Vivonne Bay shop, where residents have evacuated. ( Facebook )

Before Thursday, Kangaroo Island's fires had burnt over 170,000 hectares — more than a third of the island's terrain — and destroyed more than 50 homes.

Prime Minister Scott Morrison met with fire-affected locals on Wednesday, and also announced a funding package for the island to aid with recovery.

"You can rest assured I'm in no doubt of the devastation on the island," he said.

Earlier a fire close to South Para Reservoir broke out between Kersbrook and Williamstown in the Adelaide Hills, but has since been contained.

Police are treating that fire as suspicious and have requested anyone who may have dashcam footage from the area between 5:30am and 6:40am to contact them.