Concentrations of benzene in the air in Pancevo reached 117 micrograms per cubic meter around 11:00 pm (2200 GMT), more than 11 times the safety limit and only three micrograms shy of the threshold for mandatory evacuation, according to Radio B92.

Sulphur dioxide levels were measured at 56 micrograms per cubic meter, five and a half times above the safety norm.

Municipal officials in Pancevo sounded a general alarm at 11:30 pm, but told residents of the town, which is 15 kilometers (nine miles) northwest of Belgrade, to remain inside their homes.

The alert was removed some four hours later, and on Friday morning Mayor Srdjan Mikovic said the situation had stabilized, thanks in large part to brisk westerly winds.

A similar incident in mid-November sparked a public protest of some 1000 town residents who demanded that the state renovate Soviet-era Petrohemija petrochemical facility, blamed by protestors for the leak.

Officials at the massive chemical plant, one of the largest in Serbia, told local media on Friday that they were not responsible for the more recent gas leak, according to the Tanjug news agency.

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