Online fashion sales during April fell just below 4%, while department stores declined by 2%.
The NAB Online Retail Sales Index reported April as a tough month for retailers across the board.
The month saw a 3.8% decline in online sales in April on a month-on-month seasonally adjusted basis (mom, s.a.).
NAB chief economist Alan Oster said all retail categories contracted on a month-by-month basis, indicating broader challenges in retail.
"Our NAB Online retail sales index data indicates considerable weakness in online retail sales for April 2019.
The online retail sales, tend to be more volatile than broader retail, experiencing far greater monthly fluctuations.
"This month, both online retail and broader cashless retail series indicated very weak retail conditions.
"While yoy growth in online sales has also slowed considerably in recent months, these comparisons are made to a period of elevated sales in 2018, with major new merchants to Australia, and also pre-GST exemption effects.
"By category, department stores continued to lead yoy growth. In the month, all categories experienced a contraction in sales," he said.
Source: NAB Online Retail Sales Index April 2019
Geographically, Tasmania was the weakest during the month. Meanwhile, international retailers outpaced domestic retailers in on a mom basis.
"Tasmania, with about 2% of online retail sales, was weakest in April, after leading growth in March," Oster said.
"New South Wales, Victoria and Queensland represent over three quarters of the online market in Australia by sales value. Of these larger sales states, Queensland was strongest over the year.
"By merchant location, domestic online retailers continue to outpace their offshore counterparts, with international slowing
in yoy terms.
"However, domestic retail sales contracted in the month (down 4.4% mom, s.a.), while their international counterparts recorded mild growth (up 0.7%)."
In year-on-year terms (yoy) compared to April 2018 – one of the strongest recorded months – April 2019 remained positive, up 1.7%.
NAB estimates that in the 12 months to April 2019, Australian consumers have spent $28.98 billion on online retail, a figure which is approximately 9% of the bricks-and-mortar spend.