HONG KONG, Aug 10 (Reuters) - Hong Kong"s largest teachers" union said on Tuesday it would disband, days after it was criticised by Chinese state media and the city"s Education Bureau severed ties, accusing the group of helping to infiltrate schools with politics. The move is expected to deepen concerns over a crackdown on opposition groups in the Asian financial hub after Beijing imposed a sweeping national security law on the city last year that has stoked fears about the shrinking space for dissent. Fung Wai-wah, president of the Hong Kong Professional Teachers" Union, told a press conference the political and social situation in Hong Kong had become "drastic" and the union was unable to find a solution. "It"s a difficult decision, a helpless decision, and a heart-wrenching decision," Fung said. The union grabbed headlines at the end of July when China"s state-run media outlets Xinhua news agency and the People"s Daily condemned it as a "poisonous tumour" that must be eliminated. Hours later, Hong Kong"s Education Bureau said it would no longer recognise the opposition-leaning union, which was set up nearly 50 years ago and has around 95,000 members. It employs 200 full-time staff. The bureau said the union"s remarks in recent years were not in line with the education profession, rendering it no different than a political group, and accused it of encouraging students and teachers to take part in "unlawful activities". Students were on the frontlines of sometimes violent anti-government protests that roiled Hong Kong in 2019, with teachers among some of the thousands arrested. Hong Kong"s security legislation requires the Chinese-ruled city to "promote national security education in schools and universities and through social organisations, the media, the internet." The union, which also provides medical and welfare services to members, said it had always promoted the development of the education sector, protected teachers" rights and had not incited students to join demonstrations. Authorities have denied any erosion of rights and freedoms in Hong Kong - which returned to China in 1997 under a "one country, two systems" formula aimed at preserving its freedoms and role as a financial hub - but say China"s national security is a red line.