Police said emergency services were responding to the incident, but there was no risk of additional explosions.
At least six people died and several others were seriously injured in an explosion on Thursday at a Czech chemical plant in the northern town of Kralupy-nad-Vltavou, fire fighters said.
"We have received information about six dead and several others seriously injured," regional fire fighter spokeswoman Vladimira Kerekova said, quoted by the CTK news agency.
The Prague-Vinohrady hospital has triggered its emergency plan and is getting ready to receive a "significant number" of patients, she added.
Emergency services spokeswoman Petra Effenbergerova said six people were injured.
Kerekova said the factory belongs to the Polish firm Synthos, which manufactures synthetic rubber and polystyrene.
Two people were injured in an explosion at the same factory in 2015.
"We have launched an investigation to determine the circumstances and causes," police spokeswoman Marketa Johnova said.
She said police had learned of the explosion at 10 am local time.