Three people died when a sailing boat capsized on Friday and ran aground on a beach in central Portugal, where the coast has seen heavy swells caused by Storm Ciaran, naval authorities said.

The Danish-flagged pleasure boat capsized around a kilometre off one of the beaches at Santa Cruz, in the municipality of Torres Vedras, around 60 kilometres (37 miles) north of Lisbon, the National Maritime Authority (AMN) said in a statement.

The victims, two men and a woman whose ages and nationalities were not immediately known were found dead on the shore near the wreckage of the boat and were not wearing life jackets, Portuguese Navy spokesman Jose Sousa Luis told AFP.

The yacht had left the port of Peniche, around 30 kilometres north of Santa Cruz, on Friday morning with three people on board, he added.

Portugal was not directly affected by Storm Ciaran, which has claimed a dozen lives elsewhere in Europe.

However, the National Meteorological Institute (IPMA) has placed the country's central and northern coastal regions on red alert due to the very rough seas, with waves that can exceed seven metres (23 feet) in height.

A new storm, named Domingos by the Spanish meteorological agency, was due to pass off Portugal on Saturday and Sunday, with waves that could reach up to nine metres high, according to the IPMA.