An elderly woman died on Sunday and nearly two dozen people had to be rescued by fire crews in the western Greece city of Pyrgos after flooding caused by heavy rainfalls, authorities said.

"An 82-year-old woman was found dead in an orange grove, 22 people have been taken to safety and we have received 300 calls to drain water from buildings," a fire department spokeswoman told AFP.

She added that an operation was underway to evacuate the local hospital where around 90 people were receiving treatment according to reports.

The citizen's protection ministry said the occupants of a monastery had also been removed owing to a rockslide and that nearly all villages in the area had been declared in a state of emergency.

Over 30 fire engines were mobilised to help in addition to a search-and-rescue airforce helicopter, two boats and a crawler bulldozer, the ministry said, adding that roads were being kept open.

Greek media reported that rain in the area was the heaviest in five years, with the streets of Pyrgos submerged under one metre (3.2 feet) of water.

Local prefect Apostolos Katsifaras said efforts were being made to divert waters into the tributaries of the local Alfeios River.