China changed its law on Friday to allow judgements to be delivered in corruption and terror cases even when the suspects do not appear in court, as Beijing ramps up pressure on dozens of suspected criminals hiding overseas.

Since taking office more than five years ago, President Xi Jinping has waged war on graft at all levels of the ruling Communist Party and has pledged that the fight must continue until corruption is impossible and unimaginable for officials.

The campaign has spread beyond China's borders to graft suspects who have fled abroad, though efforts have been hampered by suspicion among Western nations uneasy about handing over suspects to a system they believe might not provide a fair trial.

Now an amendment to the criminal procedure law by China's largely rubber-stamp parliament will strengthen the overseas graft and terror fight by allowing judgements to be delivered in cases involving absentee suspects, a senior lawmaker said.

Wang Aili, director of the Criminal Law Office with parliament's Legal Affairs Commission, told a news briefing those who could be tried in absentia would include corruption suspects and those wanted for harming national security or for involvement in terror cases.

To qualify for a trial in absentia, there should be a time-sensitive urgency in handling the case and the top prosecutor would need to approve it, Wang said.

A copy of the subpoena would also need to be sent to the defendant to guarantee their "right to know," he said.

A suspect can be defended in court in such "default judgement" cases, even if they are not there, by a lawyer, who can be chosen by the defendant's close relatives or have one assigned by the state, the official Xinhua news agency said.

Once the judgement is issued, the defendant and their close relatives can appeal to a higher court, Xinhua said.

In April 2015, authorities published a list of 100 "most-wanted" graft suspects believed to be hiding overseas, many in the United States, Canada and Australia. More than half have come back to China, some voluntarily.

China has turned up the pressure on graft suspects overseas by asking their family members to contact them and encourage their return, as well as by releasing personal details about the individuals, including their addresses.

The change comes after China passed a new supervision law in March and set up a powerful anti-graft commission to extend the graft fight to all state employees, whether party officials or not.

The new system and law weaken rights protections for suspects by entrenching the use of controversial detention and questioning techniques that can allow abuse or torture, rights groups and legal experts have said.

China is also in the midst of tightening its security laws having passed a tough counter-terrorism law in late 2015, mostly to combat what it says is a serious threat from Islamist militants in its far western region of Xinjiang.

China has not provided details of how many terror suspects may be overseas, including how many ethnic Uighurs from Xinjiang the government thinks have gone to the Middle East and Afghanistan to join militant groups there.