Activists in China are calling on people to wear black on the anniversary of the bloody military crackdown on protesters in Tiananmen Square.

Beijing-based rights activist Hu Jia said he had been appealing for people to wear black T-shirts on Tuesday or light a candle at home on Monday evening to remember the event.

The Chinese government has never fully disclosed what happened and it remains a taboo topic inside the country. Hundreds, possibly more, were killed.

Hu said he felt the security around this year's event — the first since Xi Jinping became leader — was unprecedented.