Sun-loving Australians reacted angrily on Tuesday to a mid-summer bid by a conservative Christian lawmaker to ban topless sunbathing on beaches in the country's most populous state.

Christian lawmaker and veteran morals campaigner Reverend Fred Nile won backing from key politicians in New South Wales state, counting Sydney and its famed ocean beaches, to tighten existing laws covering nude sunbathing.

"The law should be clear. It must say exposure of women's breasts on beaches will be prohibited," Nile said.

Centre-left state government lawmaker Paul Gibson told the Daily Telegraph newspaper that families at the beach during the summer holidays did not want topless women.

But scores of callers to radio talkback stations complained about the plan and Leanne Peters from the ACT Nudist Club in the capital Canberra said Australia would look like a "haven for prudes" in the unlikely event that laws passed parliament.

Australians love their suntans and topless sunbathing has been common on most beaches since the 1960s. Nude beaches are also legal in every state except tropical Queensland. But the country also suffers the world's highest rate of melanoma skin cancer. A new and graphic government advertising campaign warns there is no such thing as safe tanning, building on decades of similar official warnings.

NSW Assistant Health Minister Jodi McKay said banning topless sunbathing was a step too far for most lawmakers. "We don't want to go down the slippery slope of banning activities like this. What would be next, banning breastfeeding?" she said.