The marine engineer is currently undergoing treatment at a COVID-19 care centre in Kalyan town, located about 50 km from the state capital Mumbai.
Samples of six other people, who tested positive for the coronavirus after arriving in Kalyan-Dombivli area of Thane district from different countries, have been sent for genome sequencing and the results are awaited, another official said.
The marine engineer, a resident of Dombivli town, arrived in Delhi from South Africa on November 23 and had given his samples for COVID-19 testing at the Delhi airport. He had then taken a flight to Mumbai, sources earlier said.
"He is stable and responding well to treatment," deputy director of health services, Mumbai circle, Dr Gauri Rathod told PTI.
The patient will continue to be treated at the COVID-19 care centre in Kalyan and will not be shifted elsewhere, she said.
He will undergo the treatment protocol, as prescribed for the Omicron variant, for 14 days, the official said.
Besides this patient, six other people who had travelled from different countries to the Kalyan-Dombivli area, have tested positive for the coronavirus and are kept in isolation, Kalyan Dombivli Municipal Corporation's epidemic cell chief Dr Pratibha Panpatil said.
They include four from Nigeria, and one each from Russia and Nepal. Their samples have been sent for genome sequencing and the results will be known in the coming days, Dr Panpatil said.
"The condition of all the six is stable. They are asymptomatic and none of them had come from high-risk countries," she added.
Cases of the Omicron variant have also been detected in Karnataka, Gujarat and Delhi.
According to the Centre, the countries designated as "at-risk" are European countries, including the UK, and South Africa, Brazil, Botswana, China, Mauritius, New Zealand, Zimbabwe, Singapore, Hong Kong and Israel.
Under the new norms, RT-PCR tests are mandatory for passengers arriving from the "at-risk" countries and they will be allowed to leave the airport only after the results come.
Also, two per cent of the passengers arriving by flights from other countries will be subjected to the test randomly.
With PTI inputs.