The number of cases in Singapore has more than doubled over the past week amid an explosion of infections among foreign workers staying in crowded dormitories. This group now makes up around 60% of Singapore’s cases.

Prime Minister Lee Hsien Loong said Saturday that it will take time to break the chain of transmission in the dorms. He wrote on Facebook that the vast majority of cases among migrant workers were mild, as the workers are young. Although cases in the dorms are expected to continue to rise amid ongoing virus testing, Lee said the government is building up its health care and isolation facilities to handle the load.

More than 200,000 migrant workers from Bangladesh, India and other Asian countries live in dormitories in Singapore that house up to 20 people per room with shared facilities. Tens of thousands of workers have been quarantined in their dorms, while some have been moved to safer places to reduce crowding.