Premier Nathan Rees says he hopes "criminal idiots" using explosives to blow up ATMs across Sydney injure themselves before innocent people are hurt.

ATMs at Chester Hill and Rhodes, both in the city's west, were targeted within an hour of each other early on Thursday.

The blasts bring the number of ATM attacks in Sydney to four since Tuesday, and are the latest in a spate of ATM robberies across eastern states in the past few months.

Mr Rees said it was only a matter of time before someone was hurt by one of these explosions.

"These criminal idiots who are using explosives to target ATMs, it's only a matter of time before they injure someone," he told reporters.

"With a bit of luck it will be themselves but it might also be an innocent by-stander.

"These criminal idiots will be brought to justice eventually ... they are engaging in an extremely dangerous practice."

Mr Rees said he was confident police were doing everything in their power to bring those involved to justice.

The NSW government has already offered a $100,000 reward over the spate of ATM attacks across the eastern states, with NSW Police Minister Tony Kelly on Thursday warning that those responsible will be caught.

The robbers escaped with a sum of cash after the blast at a bank ATM at Rhodes at 1.05am (AEDT) but the thieves got nothing in the attack on the Chester Hill ATM, 45 minutes earlier.

That ATM was destroyed in the blast but because it was not attached to shops there was no other damage.

The blast at Rhodes caused some damage to the Rider Boulevard building where it was located.

Witnesses reported seeing a dark-coloured Audi sedan leaving both crime scenes, police said.

No one was injured in either incident, the fourth ATM attack in Sydney since Tuesday.

Mr Kelly said police already had "a lot of information" in regard to the ATM explosions in Sydney this week, and promised that the offenders would not get away with the crimes.

"They certainly are brazen and police have a task force onto these robberies," he told reporters on Thursday.

"These people will be caught. Eventually police will catch these ATM robbers.

"It will stop."

He said offenders had a low success rate of about 30 per cent but added that they did "an enormous amount of damage".

This week the NSW government offered a $100,000 reward for information leading to a conviction for attacks on ATMs, with the Australian Banking Association pledging an additional $50,000 under an existing scheme.

"That's a significant amount of money to be able to get legally," Mr Kelly said.

"We know that people out there do have information - they may be accomplices of the people involved or they may have seen something happen."

Earlier this month, Queensland, NSW and Victorian police launched a joint investigation into possible links between more than two dozen explosive ATM robberies.

On Wednesday an ATM was blown up at Liverpool, in Sydney's south-west, and on Tuesday another was destroyed at Ruse, also in the city's south-west.

Anyone with information about any ATM robbery is urged to contact Crime Stoppers on 1800 333 000.

© 2008 AAP