A person holds two hailstones during a hailstorm at Manuka Oval in Canberra, Australia. Georgia Redmayne/Reuters

Violent hailstorms and damaging winds hit parts of New South Wales state including bushfire-affected coastal towns on Monday, but hot and windy conditions are forecast to return to many parts of NSW later in the week.

A hail storm in the national capital Canberra on Monday damaged public buildings, businesses, homes and cars, cut power to some suburbs, brought down trees, caused flash flooding and injured two people, emergency services officials said.

To the west, a 300-kilometer (186-mile) wide cloud of red dust was carried by wind gusts up to 107 kilometers (66 miles) per hour and descended on the drought-stricken towns of Dubbo, Broken Hill, Nyngan and Parkes, local media reported. Much of the dust is top soil from New South Wales state farms.

Australia on Monday boosted emergency funding for small businesses hit by bushfires that have ravaged the country for months, as the mounting costs of the disaster cast doubt on the government's ability to deliver a promised budget surplus.

The fires have killed 29 people and millions of animals, destroyed more than 2,500 homes and razed an area roughly a third the size of Germany since September, and scores of fires continued to burn on the east coast despite recent rain.

A carpet of golf ball-sized hailstones on a street after a hailstorm in Canberra, Australia. Reuters

The Australian Open got under way on schedule in relatively clear air in Melbourne on Monday, after thick bushfire smoke caused havoc with preparations last week and forced one player to retire from qualifying.

"I definitely was concerned, and am ... That is still a concern for pretty much everyone," seven-time Australian Open champion Serena Williams told reporters.

Budget repair after years of deficits was a key promise ahead of last year's election but Treasurer Josh Frydenberg sidestepped a question about whether the promised A$5 billion surplus for the year to June 2020 could be delivered.

A parked vehicle's windows are damaged after a hailstorm in Canberra, Australia. Reuters

"I'm not in a position to give a firm answer to that question because the full economic impact is still uncertain ... Our focus is not on the surplus per se," he told reporters.

The federal government has so far committed A$2 billion ($1.4 billion) for bushfire recovery, and has already trimmed its earlier forecast surplus for 2019-2020 by that amount.

Grants for small businesses affected by the fires would be raised to A$50,000 each, from A$15,000 announced earlier, and interest-free loans up to A$500,000 also would be available, the government said on Monday.

Several days of rain and cooler temperatures have reduced the number of active fires across the country's densely populated southeast and given authorities an opportunity to focus on the recovery effort.