As it happened: ASX plunges 3.1% in $56b selloff

Losses followed an overnight hiding for overheated US firms such as Tesla, Apple and Microsoft.

Wall Street's steep decline set the Asian sector up for a poor session, with Australia the region's clear laggard.

Milford Asset Management portfolio manager Mike Higgins said a US dive was probably overdue after a juggernaut run of record highs.

“There are a lot of risks in the world right now. I think a lot of people have been looking at the US for some time, and see that it has been quite unbelievable the run they’ve had,” he said.

“So they’ve been probably waiting for a pullback.”

JP Morgan Asset Management global market strategist Kerry Craig said there was no single factor that sparked the sell-off but cautioned against reading too much into near-term tremors.

"Market corrections are to be expected - a market fuelled by central bank largesse, economic surprises and record earnings beats in the last few months was never going to maintain its heady pace forever.

"When it comes to the tech sector and the other online giants that have gained so much in the last few months, there could be profit-taking as we head towards the US Presidential election in November."

Mr Higgins, however, remains cautious.

"You have a lot of people pointing to healthy pullbacks, but initial corrections that turn into bigger corrections always start off as healthy," he said.

The market started the day narrowly ahead for the week but ended up 2.4 per cent lower.

At its Friday nadir the market was as much as 3.3 per cent or $60 billion lower

Biotech CSL dropped 4.1 per cent and miner BHP fell 3.8 per cent to drag heavily, while each of the big four banks lost between 2.1 per cent and 3.1 per cent.

Tech was the hardest hit, dropping a collective 5.6 per cent to mirror the overnight fortunes of the NASDAQ giants.

Afterpay shed 6.7 per cent to $78.20, bringing its weekly losses to 11.9 per cent.