A man has died and another has been seriously injured after they became trapped under tonnes of landfill in Sydney's west on Monday.

Emergency services were called to the Dial-a-Dump site on Kangaroo Avenue at Eastern Creek just before 1pm after reports a man had been buried under the waste.

NSW Ambulance Service Inspector Michael Magyary described the scene as chaotic and tragic. He said that, initially, emergency services were only aware that one man had been injured.

That man had already been pulled clear of the waste when emergency services were told a second man was missing, Inspector Magyary said.