Trinity, the UK's biggest regional newspaper group, is expected to make an indicative offer in cash and shares, possibly as early as today, worth 200p to 220p a share.
Regional Independent Media, a privately owned company chaired by the former Conservative Party chairman Sir Norman Fowler, is meanwhile preparing to make a 220p-a-share cash bid.
The Mirror Group board, led by the chairman Sir Victor Blank and its new chief executive John Allwood, is expected to meet in the next few days to consider the offers following an auction run over the weekend by its advisers, SG Hambros.
"The phoney war has ended, things are starting to hot up," said one source close to the auction.
Mr Allwood, who took over as chief executive last month following the ousting of David Montgomery, has promised investors that he will set out Mirror Group's strategy when it reports its full-year results on Thursday.
Trinity broke off talks earlier this year on an agreed takeover of Mirror Group, which would have valued the business at around 165p a share, after a dispute with Mr Montgomery over his future role in the merged group.
RIM, which publishes the Yorkshire Post, then made an indicative cash offer of 200p, which was rejected by the Mirror board.
Trinity is counting on the support of Mirror Group's largest shareholder, Phillips & Drew, even though its cash-and-share offer may be lower than that of RIM.
Phillips & Drew, which holds a 22 per cent stake, is keen to retain a shareholding in the sector and has been told that if the Trinity bid succeeds, there will be profit enhancements through cost savings of at least pounds 15m a year.
Sir Norman's role as chairman of RIM may also count against it as the flagship title, the Mirror, supports the Labour Party.
However, one source close Mirror Group said: "The feeling is that a lot of shareholders are not desperate for paper and are rather keener on cash."
Mirror Group management is looking for a bid pitched at 230p a share.
Should Mr Allwood decide that Mirror Group has a future as an independent company, he is likely to sell L!ve TV and shelve plans for a full relaunch of its Sporting Life title.Reuse content