Its operating income fell 6 per cent to $2.282 billion while its expenses rose 7 per cent to $1.059b.
McLean said almost every customer had been financially affected by Covid-19 through either losing a job, taking a hit to their business revenue or indirectly through lower interest rates or KiwiSaver volatility.
But despite the challenging outlook and remaining uncertainty he said he was confident New Zealand remained well-positioned for recovery and Westpac NZ's healthy balance sheet would allow it to support customers and the economy.
McLean said it had supported its customers in a range of ways during the pandemic by providing mortgage and loan repayment assistance to 21,959 customers and more than $9b of new and restructured business lending.
The bank's total deposits rose 10 per cent to $71b while its net loans rose 5 per cent to $88b.
McLean said over the past year it had expanded its residential lending by 7 per cent and had helped first-home buyers into 5343 homes.
"We've increased our business lending by 3 per cent and have been one of the few banks to expand our lending to farmers and agriculture."
But falling interest rates saw the bank's margin fall 19 basis points to 1.97 per cent.
McLean said Westpac NZ was prepared for a period ahead in which interest rates could drop to record low levels.
"This may compress bank lending margins but we're in robust shape and are well equipped to weather those pressures."
He said a key concern was balancing the needs of borrowers and savers.
"We want to make sure we're passing on value to borrowers, who will appreciate reductions in repayments if their incomes have been reduced, but we also need to provide value to depositors, who provide us the funds to lend and could feel the squeeze on their savings as a result of lower interest rates."
McLean said there had been a significant increase in the number of customers banking digitally or through the contact centre since Covid-19 hit.
"That means our branch teams are now operating more flexibly. In some locations our opening hours are reduced but our team are on-site, emailing and calling our customers, reflecting the way people are choosing to bank with us."
McLean said the bank remained focused on upgrading technology, fixing legacy issues and delivering new innovative products and experiences.
Parent Westpac Banking Corporation's net profit after tax fell 66 per cent to A$2.29b and cash earnings fell 62 per cent to A$2.608b.
It will pay a full dividend of A31 cents per share.
Peter King, Westpac Group chief executive said 2020 had been a particularly challenging year and its financial result was disappointing.
"Our earnings have been significantly impacted by higher impairment charges, increased notable items and the sharp decline in economic activity.
At the same time the bank also incurred higher expenses due to increased demand due to Covid-19 as well as fixing its compliance issues, he said.
King said Austrac's proceedings had a major impact on the bank this year. It agreed to pay A$1.3b to settle the anti-money laundering case.
"We have taken accountability for our mistakes and commenced a process of fundamental change, which has included refreshing the board and management and elevating oversight of financial crime, compliance and conduct."
The bank made A$280m in payments to customers as part of its remediation programme.
