POLICE seized a Chinese student who tried to lay a wreath in Tiananmen Square yesterday. The unidentified man apparently entered the square - focus of the 1989 crackdown - at about 11 am. One witness said: ''The student was carrying an average-sized wreath of the kind used to commemorate the dead.'' Another said: ''Police stopped him and requested his identification, and he immediately produced a university identification card. ''He was then immediately bundled into a waiting police vehicle.'' Tiananmen Square has been ringed day and night by police since Monday. The incident coincided with Ching Ming, when Chinese honour their dead, and comes in a period of sensitive anniversaries, notably of the April 5, 1976, uprising after Chinese leader Zhou Enlai's death, and the April 15, 1989, start of pro-democracy protests in Beijing. Police were yesterday keeping a close watch on the families of those killed in the 1989 Tiananmen massacre. ''I haven't been able to go out for Ching Ming because there are too many police,'' said the father of one 19-year-old killed in 1989, whose urn is in Wanan cemetery at the foot of the Fragrant Hills. ''It's not that I'm afraid, just that I don't want trouble, and the mood is too tense,'' he said. The families of Tiananmen dead are close to each other and take turns visiting the cemeteries. Over Ching Ming, they meet and telephone each other. Ding Zilin, a philosophy teacher, goes often to Babaoshan and Wanan to tend the urns of young people massacred by the Army. She lost her only son, Jiang Jielian, 17. But his remains do not lie in a cemetery. Mrs Ding, who recently signed an open letter demanding democracy and the release of dissidents, keeps her son's ashes at home. ''For me, Ching Ming is every day,'' she said. Hundreds of thousands of Beijing residents gathered at Baboashan cemetery west of the capital to honour the memory of their ancestors. There were also a number of police, uniformed and in plain-clothes, carrying still and video cameras and portable telephones. Families have been forbidden from burning incense for Ching Ming because of official fears the accompanying laments might degenerate into slogan chanting against the Government. The authorities have also been confronted by increasingly active dissent, prompting a new wave of repression. As evidence of their worries, Tiananmen Square has been ringed day and night by police since Monday.