The Fraser Health Authority says more than 300 students and staff at Delta Secondary School in Ladner, B.C. are experiencing what appear to be symptoms of norovirus. 

Officials say the school is undergoing enhanced cleaning Thursday afternoon and are asking students and teachers who feel ill to stay home. 

Norovirus — once known as Norwalk virus — is highly contagious and often spreads in places like schools, cruise ships and nursing homes, especially during the winter. 

The stomach bug causes bouts of vomiting and diarrhea which can last for a few days. A new strain of the virus evolves every two or three years. 

Norovirus can be spread by sharing food or cutlery with an infected person or by touching objects contaminated with the virus.