Ukraine's Western backers are scrambling to ramp up supplies of 155-millimetre shells as they warn Kyiv faces critical shortages in the face of a grinding Russian offensive.

European officials estimate that Ukrainian forces are using up to 7,000 shells per day, while Moscow's troops are firing around 50,000.

In a bid to speed up ammunition to Ukraine, EU foreign policy chief Josep Borrell is proposing using an additional one billion euros ($1.07 billion) in joint funds to get member states to dig into their stockpiles.

The money would come from the bloc's European Peace Facility that has already dedicated 3.6 billion euros towards arming Ukraine since the start of the invasion last February, the document circulated to EU states said.

The proposal will be discussed by EU defence ministers at a meeting March 7-8 in Stockholm.

Estonia last month urged the 27-nation bloc to commit four billion euros to jointly purchasing one million shells for Ukraine.

As they look to address Kyiv's immediate thirst for ammunition, Western allies are also seeking to bolster production in their defence industries to help keep deliveries flowing further down the line.

The new EU proposal says that to help do this, the bloc should look to club together to place a "massive order" for ammunition for Ukraine and to refill its own stockpiles.

This would send industry "a clear demand signal, enabling it to ramp up its production capacity in an orderly and enduring way across Europe", the document said.

The joint purchasing would be coordinated by the EU's European Defence Agency and the aim would be to sign the first contracts as early as next month.

Eventually the bloc could set up a specific fund to buy arms together for Ukraine if EU states agree to pump in more money, the proposal said.