Pre-school staff who turned up hours ahead of their scheduled slots for Covid-19 swab tests caused long queues at Khatib MRT station on Friday, said the Ministry of Social and Family Development (MSF).
A scheduling issue involving one of the pre-school operators also contributed to the long line, it added.
The ministry was responding to widely circulated videos of the queues, which saw pre-school staff waiting for about an hour to board buses to one of four allocated swabbing centres.
Those undergoing the tests are not allowed to go to the centres themselves and must board shuttle buses at four stations, including Dover, Tampines West and Woodlands.
"The proactive testing is part of our stepped-up monitoring to provide assurance to pre-school staff and families to support the phased opening up of general services in the pre-school sector," said MSF.
"To allow for the tests to be conducted safely, we had scheduled for groups of pre-school staff to be tested in batches over the coming days," it added, urging pre-school staff to be present only at their assigned appointment slots. "There is no need to arrive much earlier."
The ministry said the frequency of buses ferrying the pre-school staff from Khatib MRT station was increased on Friday to clear the crowds quickly, adding that the queue situation eased after 11am.
In an earlier report, The Straits Times cited a circular the Early Childhood Development Agency (ECDA) sent to pre-school operators, which described the test as a precautionary measure.
Principals, teachers and the carers who look after infants and toddlers need to have a swab test done. Non-programme staff like cleaners and cooks, as well as relief and new staff starting work next month, are also required to be tested.
The tests must be completed before the centres reopen.
The Health Promotion Board (HPB) will conduct the tests until May 26 at four swabbing centres located in polytechnics, at areas segregated from the rest of the campus.
While long lines were seen at Khatib MRT station, the ministry said the situation at the other transport points was manageable and queues were cleared promptly.
The one-time swab test will be conducted for around 30,000 pre-school and early intervention staff.
A pre-school employee, who was in the queue at Khatib MRT station on Friday, said she waited for about 45 minutes to board a bus.
"It was really warm. I felt bad for those older aunties who had to wait. It was quite uncomfortable as we had our masks on," added the woman, who declined to be named. She hopes there will be more swabbing centres or waiting points.
The ministry said the ECDA and HPB are ensuring that safe distancing measures are adhered to, and older staff, who may need assistance, are attended to.
Testing at pre-schools has been prioritised as staff have close and constant contact with young children in an enclosed setting.
Earlier, a number of pre-schools had to be closed after reporting Covid-19 infections.
The tests are the latest precautionary measures implemented since January to keep pre-schools safe.
The ministry on Friday thanked pre-school staff for their cooperation and apologised for the inconvenience. "We seek your understanding as we work together with HPB to improve on the processes to ensure the safety and welfare of everyone," it added.