Two-thirds of European fund managers have warned of a bubble developing in the US government bond market, according to the latest monthly survey by Morningstar, the fund rating and research firm.

Some 40% said there is a risk that the US bond market will reach breaking point in the near future while 27% believe this is already the case. A substantial number - 40% and 46% respectively - also said there is a already a bubble or an imminent risk of one in eurozone government bonds.