The court was making a ruling on a request by Movement for Democratic Change (MDC) deputy national chairman and lawmaker Job Sikhala to drop the charges, which carry up to 20 years prison term upon conviction.
MDC vice president Tendai Biti and Zimbabwe Lawyers for Human Rights, who were present in court, said the judge in the case was forced to adjourn proceedings after teargas started filtering into the court room in Masvingo, 300 km (210 miles) south of Harare.
Police were not available to comment.
Dozens of government opponents have faced subversion charges, with critics saying this shows the government is muzzling the opposition by reverting to harsh security laws from the era of Robert Mugabe, who died last September.
Political tension has increased as Zimbabwe grapples with its worst economic crisis in a decade. (Reporting by Nelson Banya, Writing by MacDonald Dzirutwe, editing by Olivia Kumwenda-Mtambo and Angus MacSwan)
