More than 50 international media organisations have written to Turkish President Recep Tayyip Erdogan expressing deep concern about worsening conditions for journalists ahead of elections on Sunday.

Agence France-Presse is among the signatories, which also include The New York Times, The Washington Post, Germany's Sueddeutsche Zeitung and ARD television, La Stampa in Italy, Dawn newspaper in Pakistan, The Age in Australia and Buzzfeed.

The editors of the organisations listed a series of incidents over the past two months that include attacks on the offices of the Hurriyet newspaper and the assault of a leading journalist, Ahmet Hakan Coskun, as well as the arrest and detention of journalists working for Vice News.

"We urge you to use your influence to ensure that journalists, whether Turkish citizens or members of the international press, are protected and allowed to do their work without hindrance," they wrote to Erdogan.

They said the Turkish government's "failure to support and to protect journalists" during the election process "is undermining the country's international reputation and damaging its standing as a democracy".

The organisations added: "We share widespread concerns that recent events are part of a concerted campaign to silence any opposition or criticism of the government in the run-up to the election."

The editors also raised their concerns about the rise of "a culture of impunity" which deprived journalists of safeguards and said the government had failed to condemn attacks on journalists who are independent or critical.

Opinion polls predict Erdogan's Justice and Development Party (AKP) will again win the most votes but is unlikely to claw back the parliamentary majority it lost in a shock setback in June, paving the way for a shaky coalition, or another election.

The campaign has been marked by instability after devastating jihadist bomb attacks, renewed Kurdish violence and the media crackdown.