SAINT PETERSBURG (AFP) - Just when Russians thought it could not get any worse with the rouble tumbling as fast as the oil prices on which their economy depends, the people of St Petersburg are waking up to rationing.

But in President Vladimir Putin's hometown, the martyr city that survived a nearly 900-day siege in which thousands starved to death in World War II, it is not food and drink that is being rationed, but metro tokens.

In one of the most bizarre episodes of panic buying in a nation notorious for its hoarding instincts in times of trouble, people have been buying up to 85,000 extra metro tokens a day so they can save three roubles (seven Singapore cents) when the price goes up on Jan 1.

With more than 1.8 million sold so far in December the authorities had to step in and ban cashiers from selling people more than two tokens at a time.

Signs of panic-buying have emerged in recent weeks with many hard-pressed households hoarding sugar and buckwheat, one of the country's main staples, as the rouble at one point lost one quarter of its value in just two days.

Worried about rising inflation and the real value of their wages and savings plummeting, poorer Russians have been stockpiling goods they think will hold their value.

"I get the feeling people are investing in metro tokens," joked one passenger in front of the ticket desk at Prospekt Veteranov station.

Normally only around 15,000 metro tokens a day are sold in Russia's second city, but as the rouble crisis worsened that increased to between 80,000 and 100,000 a day.

The price of the tokens are set to rise from 28 roubles to 31 roubles on Jan 1.

Russia's monetary crisis - the worst in President Vladimir Putin's 15 years in power - was sparked by the fall in the price of oil, and worsened by Western sanctions over Ukraine.

The rouble has lost about 40 per cent of its value against the dollar and euro this year.