Singapore has confirmed 41 cases of the Zika virus which were locally transmitted.
All resided or worked within the same area of the state, and most of those infected were foreign construction workers, said the health ministry.
None were understood to have travelled to Zika-affected regions lately.
Zika usually has light effects but has been linked to severe birth defects.
It truly is suspected of causing a condition called a deformation in which infants are born with small heads.
Zika, which is spread by mosquitoes but can also be transmitted, was declared a worldwide public health crisis by the World Health Organization in February.
On Saturday, it declared that a 37-year old Malaysian girl had got the virus locally. She is the only confirmed female instance up to now.
Thirty six of the 41 cases announced on Sunday were foreign workers who worked in precisely the same construction site.
“We expect to identify more positive instances,” it added.