LONDON (AP) _ The British Broadcasting Corp. World Service today added 30 minutes to its daily Chinese service.

That will be in addition to the normal 2 1/2 hours of evening broadcasts in Mandarin, the main Chinese dialect, the BBC said. Student demonstrators reportedly have been playing tapes of BBC news reports over loudspeakers.

''In recent weeks we have had evidence from China of a dramatic increase in awareness of our broadcasts,'' said Peter Udell, BBC's controller of overseas services.

''This extra time on air will enable us to cover world news even more extensively - including both the latest events in China itself and international reaction to them.''

Chinese troops trying to end a seven-week student protest fired on unarmed civilians in Beijing over the weekend, and the firing has continued. Hundreds, perhaps thousands, have been killed.