Cornwall Fire and Rescue Service has requested a second pump from the National Coordination Centre in London to help with the operation to relieve flooding in the decommissioned Wheal Jane tin mine near Truro.
The Centre has also been asked to send a high volume pump advisor to help.
There are fears that if levels continue to rise it could lead to pollution of the River Carnon and the Fal Estuary.
Levels are being monitored by the Environment Agency who are working with the Coal Board and plant operations to relieve the situation. The Public Health and Protection Agency is also assisting while Maritime Services are working with local oyster fishermen.