The blast occurred at 2.24 a.m. Moscow time (22:24 GMT) in the town of Kirishi. One person died in the fire following the blast, and four others were hospitalized with severe burns and other injuries, a health official said.
"Four of the injured were brought here, those whose lives were in danger. They are in intensive care with extensive burns," a health official said.
The explosion destroyed the compressor station and damaged other facilities in the refinery owned by oil company Surgutneftegaz. The plant accounts for about 30% of Russia's low-sulphur fuel output, mainly consumed in northwestern Russians regions and exported to Western and Eastern Europe.
Cleanup work is continuing at the site. The industrial safety regulator Rostekhnadzor and local prosecutors are investigating the explosion.
The regional prosecutor's office said the blast was probably caused by technical problems.
"According to the preliminary version, the explosion was caused by a technical failure," the office said.
This is the second accident at the refinery this year. A fire in February covered a total of 400 sq m, but no one was killed or injured. Unauthorized welding was reported as the cause of the blaze.
