Lockout laws and restrictions on the sale of alcohol in late-night venues might be controversial but they substantially reduce rates of violence, a major international review has found.

The verdict from researchers at Melbourne's La Trobe University is based on a comprehensive review of 21 studies, including seven from Australia, that examined the impact trading hours at licensed premises have on alcohol-related violence.

"Increasing trading hours tends to result in higher rates of harm, while restricting trading hours tends to reduce harm," the researchers wrote in a paper published in the Sax Institute's Public Health Research & Practice journal on Friday.

"The evidence of effectiveness is strong enough to consider restrictions on late-trading hours for bars and pubs as a key approach to reducing late-night violence in Australia."

Their finding comes amid calls for the NSW government to ease its controversial 1.30am lockout laws and 3am last drinks rules at live entertainment venues in Sydney's CBD and Kings Cross.

Former High Court judge Ian Callinan made the recommendation in an independent report that also suggested the state-wide ban of takeaway alcohol after 10pm be relaxed by an hour as it has little impact on violence or anti-social behaviour.

Queensland in July also introduced new liquor laws which prevent licensed premises operating after 2am unless they are within a designated 'safe night precinct', and ban the sale of strong drinks after midnight. Lockout laws start in February.

Critics argue the laws destroy nightlife activities and should be dumped, while the state governments say they are needed to help reduce alcohol-related attacks.

The La Trobe University researchers said Australian studies that had found the laws help reduce assaults were backed up by others from Norway, the United States and Canada.

One study of Newcastle's 1.30am lockout laws and a ban on the sale of shots after 10pm found that assaults dropped 37 per cent. There were similar findings in Sydney, with assaults down about 30 per cent.

The most comprehensive study was in Norway, where a one-hour change in trading hours for 18 bars was associated with a 16 per cent change in recorded assaults.

A study on extended trading hours in two of Amsterdam's entertainment precincts had similar findings - a 34 per cent rise in ambulance calls to alcohol-related incidents.

However, there was contrasting evidence from the removal of set licensing hours for pubs in England and Wales.

While one study found some increases in harm after trading hours were relaxed in 2005, subsequent studies did not.

Another Canadian study found no impact on assault rates in two cities in Ontario after a one-hour extension of trading hours there.

While there were fewer studies on takeaway alcohol, Swiss and German researchers found evidence that reducing sales late at night can reduce harm, particularly among young people.