By Linda Hutchinson-Jafar PORT OF SPAIN, Trinidad (Reuters) - Trinidad and Tobago will impose a state of emergency from midnight to contain an increase of COVID-19 cases and related deaths, Prime Minister Keith Rowley said on Saturday. Rowley also imposed a curfew from 9 p.m. to 5 a.m. local time, with some exceptions to essential services including the energy sector, supermarkets, and pharmacies. The twin island state was experiencing a third wave of COVID-19, Rowley said. Seven hospitals caring for COVID-19 patients are at a critical stage of 73% overall occupancy, Principal Medical Officer Dr Maryam Abdool-Richards added. With a population of more than 1.3 million people, Trinidad and Tobago has registered 15,375 infections, 5,214 of them active, and 265 deaths, health ministry data showed. Health officials have cited a highly transmissible Brazilian variant, first identified in a Venezuelan migrant, as a factor in the increase in cases. Some 60,500 people have received their first vaccine dose but only 1,000 of these have received a second dose. (Reporting by Linda Hutchinson-Jafar in Port of Spain Trinidad; Writing by Stefanie Eschenbacher; Editing by Chris Reese)