Five people were injured, two seriously, by a chemical explosion at a research facility of the US pharmaceutical company Pfizer in Connecticut.
The explosion occurred this afternoon in a warehouse where a number of chemicals were stored, a spokesman said.
"The exact cause of the blast is not yet known, and there are federal agents there now conducting investigations."
The fire triggered by the explosion was restricted to the one warehouse and extinguished by the Pfizer facility's own fire crew. Two of the five employees injured in the incident were taken by helicopter to a nearby hospital, one of them with severe burns.
About 6,000 people are employed at the Groton, Connecticut facility and four buildings in the complex were evacuated in the wake of the explosion.