The hundreds of wildfires that have swept western Russia are expected to cost $15 billion US, or about one per cent of the country's gross domestic product, a Moscow newspaper said Tuesday.

The business daily Kommersant also said a rise in grain prices would likely lead to a spike in inflation and stifle growth.

Russian Prime Minister Vladimir Putin sits in the co-pilot's seat in a water bomber flying 180 kilometres southeast of Moscow Tuesday. (Alexei Nikolsky/Associated Press)

The government has yet to release any damage estimates.

The fires have cloaked Moscow in suffocating smog, amid the hottest summer since record-keeping began 130 years ago.

A widespread drought has cost Russia more than a third of its wheat crop and prompted the government to ban wheat exports for the rest of the year.

Another business daily, Vedomosti, quoted Kremlin-linked political analyst Gleb Pavlovsky as saying the Russian leadership was unprepared for the fires.

An opinion poll suggested there's been a drop in approval ratings for both Prime Minister Vladimir Putin and President Dmitry Medvedev.

A nationwide poll of 2,000 conducted by the Public Opinion Foundation earlier this month showed Putin's approval ratings dropping from 63 to 61 per cent compared with a survey in late July, while Medvedev saw his popularity drop from 57 to 52 per cent.

The margin of error for the poll was about plus or minus 3 percentage points.

With files from The Associated Press