By restoring indefinite detention without trial, Malaysia has reopened the Pandora's Box for politically-motivated and abusive state actions, Human Rights Watch (HRW) warned today.

The organisation described the passing of the Prevention of Terrorism Act (Pota), which grants authorities wide detention powers, as a "giant step backwards" for human rights in Malaysia.

HRW Asia Division deputy director Phil Robertson ( right ) said while the law was introduced to counter terrorism, it raises fear that Putrajaya would abuse it to silence dissent.

"Passage of this legislation raises serious concerns that Malaysia will return to practices of the past when government agents frequently used fear of indefinite detention to intimidate and silence outspoken critics.

"By restoring indefinite detention without trial, Malaysia has re-opened Pandora's Box for politically motivated, abusive state actions that many had thought was closed when the abusive Internal Security Act was revoked in 2012," Robertson added in a statement today.

He said Pota, which was passed at 2.25am today, with Parliament having suspended its clock to allow for debate past midnight, called into question the government's commitment to basic rights that are critical to the rule of law in a functioning democracy.

"By stripping accused persons of the right to trial in a court, access to legal counsel and other legal protections if they are accused under the very broad provisions of this law, the government is continuing its slide into rights-abusing rule," Robertson said.

Just as rights groups condemned the passing of Pota in the wee hours of the morning, the government at the Parliament session today tabled amendments to the Sedition Act to increase punishment from a maximum of three years to 20 years.

The amendments also seek to deny bail to those charged under the Sedition Act.