Two-thirds of its 1,400 workers staying at Westlite Jalan Tukang dormitory have taken their serology tests to check for Covid-19 antibodies, Sembcorp Marine said in an update on Friday.

About 53 per cent - roughly 750 workers - are now in Singapore's national vaccination registry and recognised as vaccinated, the company added, just over a week after tempers flared at the dorm over bad food and delays in the conveyance of Covid-19-positive workers to care facilities.

The company said it is making vaccinations - including with Sinovac and Sinopharm vaccines - available to its workers who have not met the criteria for registration in Singapore's National Immunisation Registry, and that a vaccination exercise for these workers has been ongoing since last Tuesday.

It has also started an investigation into allegations of foreign objects in the food it catered for its workers. This came after workers alleged that they were given spoilt food, with photos circulating online that showed packed meals that contained insects, worms and bits of newspaper.

"While we have yet to find evidence to substantiate the claims, we are treating the matter seriously," it said.

The company said it has since organised additional engagements for its workers to provide direct feedback to its caterer, and that it has worked with the caterer to "make specific improvements based on the workers' feedback".

Sembcorp Marine's vice-president of human resource operations Koh Guat Siew said the company had been actively engaging its most recent batch of workers since July, a month after they arrived in Singapore.

"In our initial interactions, the workers had provided feedback on food preparation and food hygiene," she said. "These are important concerns, and immediate steps were taken to rectify the issues with the caterer."

In a video sent to the media, a chef from Sembcorp Marine's caterer said he has held engagement sessions with the dorm's Chinese residents to better understand their meal preferences.

He said: "As these workers come from different parts of China, we had to reach common ground to cater to their taste buds. We understand too that the food now is better received by them, and we'll ensure that this continues."

Sembcorp Marine did not name its caterer, but the video showed workers from meals provider Catering Solutions unloading and distributing packed meals to workers at the Jurong dormitory.

The company said that many of its workers have concerns, as they are unfamiliar with Singapore's public health protocols. It has since stepped up engagement with its workers to explain them as well as the vaccination registration process.

Last Tuesday, it invited the medical director for the Ministry of Manpower's Assurance, Care and Engagement Group, Dr Lam Meng Chon, to speak to its workers on current public health measures, and address their questions and concerns, it said.