Japan's lower house of parliament passed a controversial new state secrets bill Tuesday, which critics say is draconian and will impinge on press freedom and the public's right to know.

After a morning of debate, the ruling bloc with support from one opposition party voted for the bill, which would give Tokyo far broader powers in deciding what constitutes a state secret, and severely punish those who leak the information.

The legislation was sent to the upper house for more debate.

That chamber is also controlled by the ruling bloc, which is trying to enact it by the end of the current Diet session on December 6 with approvals from both chambers.

"This is a law that would ensure safety of the Japanese people," Prime Minister Shinzo Abe told reporters after the bill's passage through the lower house.

"Through debates at the upper house, I will do my utmost to ease concerns that the public may have," he said.

The hawkish premier insisted that the bill would neither restrict freedom of the press nor encourage authorities to "arbitrarily" designate information as restricted.

"Frankly speaking, there is misunderstanding," Abe said earlier in the day.

"I want to firmly say that it is obvious that normal reporting activity of journalists must not be a subject for punishment under the bill."

Abe's ruling coalition has argued that the legislation is crucial for Japan to enhance its national defense, despite growing concerns among major opposition parties and the public.

Thousands of demonstrators have hit the streets to register their anger at the bill, which comes amid worldwide debate over government secrecy in the wake of the Edward Snowden affair.

Under the proposals, information related to defense, diplomacy, counter-intelligence and counter-terrorism can all be classified as a state secret, at the behest of politicians.

Critics argue that the bill could mean far more information being kept from the public, with little real oversight.

The legislation is aimed at plugging Japan's notoriously leaky bureaucracy after years of complaints from chief ally the United States, which has been reluctant to pool information.

If the law is passed, public servants who give away state secrets could be jailed for up to 10 years. The present maximum is one.

Official intelligence-gathering has come under the spotlight since ex-CIA employee and NSA contractor Snowden fled to Hong Kong and later Russia with a trove of classified US documents about surveillance programs. (AFP)