Big Four professional services firm Deloitte has laid off about 700 staff and partners in Australia following a steep reduction in revenue due to the COVID-19 crisis, following a similar move by PwC last week.

The firm would not disclose how many of the layoffs will affect Deloitte's legal arm but said the cuts would be made across most of its business units.

The layoffs equate to about 7% of the 10,000 employees in Australia and follow a 19% drop in revenue in May compared with the year before.

The Big Four firm said it expects to see a decrease in revenue continue for at least the first quarter of the new financial year, which starts in July.

"Despite significant cost-saving measures being taken across the firm, a reduction in partner and staff numbers was unfortunately required to re-balance the demand and supply side of the business and protect the long-term sustainability of the firm," the firm said in a statement.

It also said the cuts will affect most business units and internal client service departments, with greater reductions in the consulting and advisory parts of the business. The firm would not comment on how many staff will be asked to leave its tax and legal division.

PwC said last week it would lay off about 400 staff—equivalent to 5% of its workforce in Australia, following a drop in revenue over the past three months.

"We want to ensure our business is strong, is set to grow successfully and sustainably and is focused on our clients and their needs. Equally, these are difficult decisions and we are saddened that making structural changes in some of our businesses will cause some difficult impacts," PwC CEO Tom Seymour said in a statement.

The firm would not comment on how many legal services staff would be laid off.

The Big Four firms all previously took measures to combat the economic impact of the virus.

KPMG Australia's equity partners agreed to forego a partner distribution payment due in mid-April and also agreed to take a pay cut.

EY's Oceania business enacted a hiring freeze, reduced partner drawings, and cut staff pay and hours.

And PwC Australia reduced its partner drawdowns and cut most employees back to a four-day week, including those at PwC Law.