The measures, announced on Sunday by Prime Minister Kamla Persad-Bissessar, include an overnight curfew.
Ms Persad-Bissessar said they were taking action in what she called "hot spots" as part of a wider effort to tackle "wanton acts of lawlessness".
The opposition said it was a "panic response" by the government.
The declaration of emergency rule in six areas, which will last 15 days, came after the country saw 11 murders in just a couple of days.
Ms Persad-Bissessar said the killings were a reaction by drug gangs to recent major seizures by the police of consignments worth millions of dollars.
"These large sums of money simply do not disappear from the drug trade without consequences," she said.'Thugs'
The aim of emergency rule was to halt the current spike in gang activity and crime in general in the shortest possible time, the prime minister said in a televised address.
"The nation will not be held to ransom by marauding gangs of thugs bent on creating havoc on our society. The limited state of emergency in hot spots across Trinidad and Tobago is merely part of a larger aggressive reaction response by the government."
The measures include a 21:00 to 05:00 overnight curfew, as well as increased powers for police to conduct searches and make arrests.
Opposition leader Keith Rowley said the measure showed that the government had no plans to deal with rising crime.
"Our initial thought is that this is a panic response which has not been the product of any serious deliberations," he told local radio.
The measures took effect after being approved by President George Maxwell Richards..