SECURITY at two of China's main airports, Beijing and Shanghai, has been noticeably tightened after the spate of hijackings to Taiwan last year but inspection procedures still fall well short of international standards. Special security channels have been set up at Beijing's Capital Airport for passengers travelling on domestic flights to Xiamen and other cities in the vicinity of Taiwan. Additional staff have been brought in to ensure that rigorous checks of passenger's baggage and clothing are carried. Nearly all of the 10 hijackings last year have been on domestic flights over the southeast coast of China. A businessman from Xiamen who regularly travels to Beijing said he welcomed the increased security even it did mean getting through ground formalities took longer than usual. ''We are not used to having our baggage turned out and rummaged through by security staff and I must say it is a little inconvenient but I suppose it is necessary now,'' he said. ''I know two people who have been on hijacked flights last year. It is certainly getting out of hand.'' Security on ''low risk'' flights has also been stepped up with new restrictions on the amount of hand baggage and the types of articles which can be brought on board. However the restrictions on baggage size are not being enforced and security staff appear to be highly selective in who they single out for attention. At both Shanghai and Beijing airports this week, I was able to carry on a case containing a laptop computer, tape recorder, spare batteries, wiring and other suspicious objects without so much as a bat of an eyelid from security staff. Staff at the airports said they had been instructed to concentrate on ''suspicious looking mainlanders'' and were quite content to let people who did not fit into that category pass through without any trouble. Senior civil aviation officials have admitted that incompetent staff were partly responsible for the dramatic rise in air piracy last year and that much more training and discipline will be necessary if airport security is to be brought up to international standards.