China's Fosun International Ltd has upped its bid for Portugal's Espirito Santo Saude (ESS) to 4.82 euros a share or 460.5 million euros ($584 million) in total, stepping up the battle over the hospital business of the indebted Espirito Santo family.

Portugal's CMVM market regulator said late on Friday it registered the all-cash offer by conglomerate Fosun's Portuguese insurance unit Fidelidade, while also extending by a week to Oct. 10 a rival offer by Mexico's Grupo Angeles, the first to bid for ESS.

Angeles initially offered 4.3 euros a share for the company on Aug. 19 and later raised its bid to 4.5 euros per share.

Fosun's previous 4.72 euro bid had already trumped Angeles' bid, but not an offer by U.S. UnitedHealth Group to bankrupt Espirito Santo family company Rioforte for its 51 percent stake, pitched at 4.75 euros a share.

If successful, the offer from UnitedHealth, which has several healthcare facilities in Portugal via its Brazilian unit Amil, would make a mandatory offer to minority shareholders at the same price.

The beleaguered Espirito Santo family's main holding companies need to sell assets after filing for creditor protection in July under a mountain of debt.

Another bid, by Portuguese healthcare firm Jose de Mello, failed Friday's CMVM registry deadline because competition authorities were unable to give their opinion on the offer. The company said it disagreed and still wants to take part.

The takeover battle has helped drive ESS shares up nearly 56 percent since their market debut in February, far outperforming the wider market. Its Friday closing price of 4.87 euros, a premium to existing offers, suggests some investors see scope for yet higher bids.

Fosun has been increasingly active globally, snapping up Portuguese insurer Caixa Seguros e Saude, of which Fidelidade is part, in January and upping a bid for holiday group Club Mediterranee SA this month.

Fosun is also looking to boost its private healthcare business, a growing area in China as the government looks to open the sector up to private capital.