PowderJect Pharmaceuticals plc confirmed that it has received preliminary offers from "certain parties" regarding the potential purchase of the company, although it said it was too early in the process to say whether any offer would actually be made.

UK papers reported that Chiron Corp. made on offer of 500 pence (US$7.74) per share, or nearly $700 million, for the company. The Financial Times, quoting a person familiar with the talks, reported PowderJect plans on rejecting the offer, saying it was an "opportunistic attempt to buy the company at a low price."

PowderJect's stock soared on the rumors, climbing 162.5 pence, or 63.7 percent, to close at 415 pence.

PowderJect, of London, is a vaccines company. Its two subsidiaries, Evans Vaccines and SBL Vaccines, market seven vaccines between them, including TB Vaccines; Arilvax, a yellow fever vaccine; and Fluvirin, for influenza.

Chiron, of Emeryville, Calif., has three aspects to its business. It focuses on biopharmaceuticals, blood testing and vaccines. Its vaccines division, Chiron Vaccines, is the fifth largest vaccine business in the world and offers more than 30 vaccines for adults and children. It offerings include Menjugate, a conjugated vaccine against meningococcal C disease; Fluad, an adjuvanted flu vaccine; Begrivac, a preservative-free flu vaccine; and Encepur, a vaccine against tick-borne encephalitis. The company did not return phone calls seeking comment.

Chiron's stock (NASDAQ:CHIR) fell 2 cents Monday to close at $42.49.