The accident happened in the basement of a hotel in Tambon Patong of Krathu district at 7:20am.
The killed worker was identified as Suthep Lookyi, 32, who worked as a room boy for the hotel.
Other workers said Suthep accidentally dropped a room key into the elevator chamber and tried to retrieve it from the basement floor without informing the elevator service department first. The counterweight crushed him when a hotel guest then used the elevator.