People protest against Japanese Prime Minister Shinzo Abe's controversial security bills. (AFP Photo)

Crowds took to Japan's streets Wednesday to protest legislation expected to be passed this week that could see troops fight overseas for the first time in 70 years, despite mass public opposition.

Hundreds of people holding placards saying "No war" and "Don't ram through the legislation" faced a line of police outside a hotel in Yokohama, a city south of Tokyo, where lawmakers gathered for a public hearing on the bills.

Demonstrators later began blocking the roads, chanting anti-war slogans and trying to stop lawmakers from driving away after the debate.

The protests are the latest show of public anger at Prime Minister Shinzo Abe's plans to expand the role of Japan's military on the world stage.

Tens of thousands of people are also expected to gather outside parliament later Wednesday as a special committee debates the bills -- the last step before they go to the upper house plenary session, where they are expected to be pushed through by the ruling coalition's majority.

Opposition parties are planning actions to try block the legislation, including censure motions to try to embarrass the government into submission, but these are not expected to stop the bill being passed.

Under the proposed new laws Japan's army, known as the Self-Defence Forces, would be able to go into battle to protect allies even if there was no direct threat to the country or its people.

Although the current post-war constitution -- which barred troops from taking part in combat except in pure self-defence -- was imposed by US occupiers, many Japanese feel strongly any change would alter the country's pacifist character.

Many legal scholars have said the changes are unconstitutional, and critics worry they would drag Japan into American wars in far-flung parts of the globe.

Abe and his supporters say the bills are necessary to deal with a changing security environment marked by an increasingly assertive China and unpredictable North Korea