The mud outburst at a station of the subway Line 4 took place yesterday, trapping eight workers, the Hangzhou Subway Group said in a statement.
Four workers were rescued soon and rushed to hospital.
Of them, two have been discharged from hospital and the other two are still being treated.
According to Hangzhou Subway, the foundation pit of the subway was not affected by the accident.
But the group said it will closely monitor weather conditions as typhoon Nepartak approaches and pump water from the pit if necessary to ensure the safety of the subway project and people around, state-run Xinhua news agency reported.