SHANGHAI, July 1 (Reuters) - China's top social media companies have condemned online hate speech targeting Japanese, delivering a vigorous response to comments triggered by a knife attack last week that killed one person and injured a Japanese mother and child.

Such waves of sentiment, and a vocal nationalist element, are not uncommon, but companies from WeChat-owner Tencent , to TikTok's ByteDance-owned sister-site Douyin, Weibo and NetEase, condemned last week's remarks.

"These comments have disrupted the positive and peaceful atmosphere of the platform and even incited unlawful behavior," Douyin said in an online post on Sunday, citing "extreme and erroneous statements" that were "promoting xenophobia."

In the latest of a series of knife attacks nationwide, a Japanese mother and her pre-schooler were injured in the eastern city of Suzhou while waiting for a school bus. A Chinese bus attendant died of injuries suffered during a bid to intervene.

Anti-Japanese sentiment in China stems from bitter memories of the neighbor's World War Two aggression, leading some to celebrate the targeting of its citizens in the attack.

The extreme comments on Douyin stood out from the flood of tributes that praised the heroism of the 55-year-old bus attendant, Hu Youping, it added.

Tencent said it had tackled 836 instances of related content that infringed its rules.

"Some netizens incited confrontation between China and Japan, provoked extreme nationalism, and concocted various extreme remarks online," it said in online comments on Saturday.

State media also condemned the online hate speech.

"We will also not accept the hype of 'xenophobia' and hate speech by individuals," the government-controlled People's Daily said in an editorial on Friday. "This is unacceptable to mainstream Chinese society and us Chinese." (Reporting by Casey Hall; Editing by Clarence Fernandez)