Australian card transaction activity fell slightly in late August from a historical high earlier in the month, although quarterly growth momentum has continued to strengthen and is now in the 1.3% to 1.5% range, Westpac said in a Thursday report.

The Westpac-DataX Card Tracker Index fell to 158.1 in the week ended Aug. 29, a decline of 1.1 points from the 159.2 reading for the week ended Aug. 8, the report showed.

While the quarterly growth marks the strongest pace of expansion since late March, more of the gain now appears to be coming from higher fuel spend as petrol prices have again topped AU$2 per liter following the end of temporary excise tax cuts, the bank said.

"The latest card tracker data shows a pick-up in nominal spending growth momentum but a significant part of the lift, potentially up to half, looks to relate to higher prices rather than volumes," Westpac said.

Meanwhile, monthly growth momentum saw some softening, tracking a milder 0.2% gain for August, down from the 0.7% to 0.9% pace registered from May through July.

Victoria continues to lead other regions, with quarterly growth running at 2.2% compared with growth rates of 0.9% to 1.5% across other major states, the bank said.