Investors were watching early exchanges in the last presidential debate before the US election on Friday as the Australian share market lagged due to miners and healthcare.

The S&P/ASX200 benchmark index was lower by 15 points, or 0.24 per cent, to 6158.8 at 1200 AEDT.

The All Ordinaries was down by 16.2 points, or 0.25 per cent, to 6367.5.

Materials was down 0.91 per cent, while healthcare was lower by 0.6 per cent.

Plenty of attention was on the contest between US President Donald Trump and Democratic rival Joe Biden.

Early on, Biden renewed his attacks on Trump’s handling of the coronavirus pandemic, seeking to bolster his opinion polls lead with 12 days to go until the November 3 election.

Trump defended his approach to the outbreak and claimed the worst of the pandemic was over.

Overnight, US markets closed higher as investors remained optimistic of more fiscal stimulus to support a pandemic-damaged US economy.

Unemployment showed fewer Americans filed for support but the figure remains high at 787,000 people.

Despite the good lead, the ASX trended lower from the start of trade.

Domestically, Victorian authorities were monitoring coronavirus cases in Melbourne’s northern suburbs.

They had for two weeks been monitoring the outbreak, which affected 36 people, and considered it contained until a student became infected.

The child was the state’s only virus case in the previous 24 hours.

Meanwhile Qantas has suffered a $100 million hit to its first quarter earnings after several states closed their borders in July in response to Victoria’s virus concerns.

Chief executive Alan Joyce said the states’ decisions had delayed Qantas’ recovery.

Shares were higher by 2.48 per cent to $4.54.

National Australia Bank said its second half cash earnings will take a $264 million hit from provisions for customer and payroll remediation and an impairment of property assets.

The charges will reduce net profit by $450 million.

Shares were up by 0.56 per cent to $19.52.

Among other banks, ANZ gained 0.76 per cent to $19.65, the Commonwealth improved 0.18 per cent to $69.46 and Westpac was better by 0.56 per cent to $18.70.

In mining, BlueScope Steel bucked the sector and rose 11.73 per cent to $16.04 after reporting it expected a 30 per cent lift in first half earnings.

BlueScope said it expects earnings before interest and tax of about $340 million after strong demand in the three months to September 30.

Among other miners, BHP dropped 1.34 per cent to $35.99, Rio shed 1.37 per cent to $94.90 and Fortescue slipped 0.62 per cent to $16.68.

The Aussie dollar was buying 71.23 US cents at 1200 AEDT, higher from 70.96 US cents at the close of trade on Thursday.