The Jamaican army has been called in to restore order in the capital Kingston.
The move comes after 20 people were killed in gun battles over the weekend between security forces and residents of a poor Kingston neighborhood.
Jamaican Prime Minister Mr P J Patterson also said the former British colony was asking other countries for help to combat the violence.
Police said 20 people were confirmed dead and 30 injured in the violence, which began after a police raid on Saturday for illegal weapons in west Kingston, an area that has seen growing gun violence in recent months.
Soldiers joined police on the weekend weapons raid, but Mr Patterson's announcement today signalled a broad deployment of the army to try to restore calm.
He spoke hours after a policeman was shot and burned to death in his car in Kingston, amid mounting tension in the wake of the weekend gun battles. At least one police officer and a soldier were reported killed in those shootouts.
The violence had not spread to the popular resorts of Montego Bay, Ocho Rios and Negril, the heart of the $1.3 billion tourism industry that contributes 15 per cent of Jamaica's gross domestic product.
Jamaica has a history of sporadic violence between gangs linked to political parties. It also suffers from crime, related to the drug trade and gang turf wars. More than 320 people have been killed this year, say police.