A LARGE number of workers are trapped in lifts and 7000 others have been evacuated after an explosion rocked an office block in Melbourne's CBD this afternoon. About 7000 workers have been evacuated from two buidlings at 570 Bourke St and 600 Bourke St following the explosion at an electricity substation behind the 35-storey office tower at 570 Bourke St. Five workers are believed to be trapped in lifts at 570 Bourke with a yet-to-be determined number trapped at 600 Bourke. The fire brigade is in contact with the trapped workers via mobile phone and they are reported to be...