The Northern Marianas Department of Public Health is urging people with respiratory problems to remain indoors after volcanic haze from Anatahan island.
The government issued an alert against the sulfur winds that enveloped the islands of Saipan and Tinian yesterday.
Anatahan is a small volcanic island 120 km north of Saipan.
No private and public schools were closed, but outdoor activities were cancelled.
According to the CNMI Emergency Management Office, the volcano on Anatahan has been putting out gas and steam lately.
Last month, the Governor extended again the emergency declaration on Anatahan, saying the island is still unsafe for human habitation.
He ordered all travel to the island restricted with the exception of scientific expeditions.
The emergency declaration for Anatahan has been in place since May 13, 2003.