TOKYO (Reuters) - Laws loosening the limits of Japan’s pacifist constitution on its military took effect on Tuesday as surveys showed the public remained divided over a change that allows Japanese troops to fight overseas for the first time since World War Two.

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Prime Minister Shinzo Abe has said the security legislation, the biggest change in Japan’s defense policy since the creation of its military in 1954, is vital to meet new challenges including a rising China.

Critics say the changes, which triggered demonstrations ahead of their enactment last September, violate the pacifist constitution and increase the risk of involvement in foreign wars. Opposition parties plan to campaign for the laws’ repeal in an upper house election in July.

“The security environment surrounding our country is increasingly severe,” Abe told reporters at a news conference after parliament approved the state budget.

“In a world where no one nation can defend itself on its own, this legislation will help prevent wars,” he said.

A crowd protested against the bill outside parliament as Abe spoke, holding placards saying “Oust the Abe Administration” and “We won’t condone war”.

Japan’s ally the United States has welcomed the changes, which allow the military to fight in aid of friendly countries that come under attack if Japan’s security is also threatened.

But China, where bitter memories of Tokyo’s wartime aggression run deep, has repeatedly expressed concern about the legislation, based on a controversial re-interpretation of the pacifist constitution.

The main opposition Democratic Party and other opposition groups are raising the issue ahead of the upper house election amid speculation Abe may also call a snap poll for the powerful lower chamber. How much traction the issue has is unclear.

A voter survey by the Yomiuri newspaper published on Tuesday showed 47 percent did not approve of the changes against 38 percent who did. That compared with 58 percent who opposed the legislation last September versus 31 percent who approved.

However, in a separate survey by the Nikkei business daily, only 35 percent said the legislation should be repealed, while 43 percent said it should remain in place.