Malaysia flag seen on the top of Palace of Justice building's dome.

Malaysian authorities are tracking around 5,000 citizens across the country believed to have been potentially exposed to the coronavirus at a religious event in the outskirts of the capital Kuala Lumpur, the health ministry said on Wednesday.

The contact tracing was initiated after neighboring Brunei reported its first case of coronavirus infection on Tuesday, a 53-year-old man who had attended the same event at a mosque between Feb. 27 and March 1, the ministry said in a statement.

"Based on preliminary information, the religious event involved an estimated 10,000 people from several countries including Malaysia," the ministry's Secretary-General Noor Hisham Abdullah said.

"The health ministry urges all who had attended the event to cooperate with health officials to ensure COVID-19 does not continue to spread in their communities."

Malaysia reported 20 new cases of coronavirus infection on Wednesday, bringing the cumulative tally to 149.

The new cabinet under Prime Minister Muhyiddin Yassin, which held its first meeting earlier the same day, imposed an entry ban on all Iranian, Italian and South Korean nationals due to the coronavirus outbreak in those three countries.

Malaysians returning from Iran, Italy and South Korea would be quarantined for 14 days, Health Minister Adham Baba said.