SINGAPORE - The fire that broke out at a Punggol construction site on Tuesday (May 16) appeared to have been caused by the burning of rubber.

The rubber was meant for water retention tanks that were to be installed in the carpark of the Global Indian International School (GIIS) site, the school said in a statement on Wednesday.

Two workers were taken to Changi General Hospital to be observed for smoke inhalation after they were trapped in a gondola during the blaze, which was extinguished at about 5.30pm.

They are fine and have been discharged with two days of medical leave, the school said.

It added that the fire was confined to a 30m by 50 m area on level one of the building.

The school thanked various parties in its statement, including the Singapore Police Force, Singapore Civil Defence Force, the Punggol Community Centre and the Building and Construction Authority (BCA).

"A large delegation of the GIIS Project Team was on site right even prior to the start of the incident and stayed back on site until 9pm till the last batch of workers left the site," said the school.

"Last but not least, we wanted to thank our community of parents, vendors, partners and friends for the overwhelming messages of support and encouragement, we feel truly humbled by your generosity and kindness."

A spokesman for the school, which currently has three campuses in Singapore, said on Tuesday that its Punggol campus was scheduled to open early next year.

"The school... currently does not expect a delay in construction; it's working with the authorities to investigate the matter," she added.

A BCA spokesman said on Tuesday that a professional engineer had inspected the site, and assessed the structural stability of the building to be unaffected.

The Ministry of Manpower said on Tuesday that it was investigating the incident.