KOBE -- City officials Thursday began surveying the sea bottom off Port Island to prepare for construction of Kobe airport, scheduled to begin in mid-September, while airport opponents continued to call on the mayor to stop the project.

A survey of nearly 360 hectares of seabed began at about 8 a.m. when a tugboat pulling an oceanographic research ship moved into position.

The ship will take water samples, and will explore the seabed for hidden metal objects, including, officials said, possible unexploded bombs from World War II.

City airport official Shuso Mizuma said the survey is expected to be concluded at the end of the month.

On Wednesday, airport opponents sent the results of an informal vote on the airport plan to Kobe Mayor Kazutoshi Sasayama. Led by lawyer Rokuro Kitayama, the group demanded the city let it present the results directly to Sasayama but was refused. After a heated discussion in front of City Hall, the group turned the results over to a city official.

"It's a shame that the mayor is ignoring the voices of nearly 300,000 people," Kitayama said afterward.

Earlier this month, the group announced the results of an informal poll taken among more than 310,000 residents of Kobe and surrounding areas. Of the total, 290,000 people, or more than 90 percent, said they were against the airport.

Kobe city officials said the poll had no legal basis and that the airport had already been approved by City Hall. In December, Kobe's city council voted down a proposed plebiscite after nearly one-third of the city's eligible voters had signed a petition asking for a vote on the issue.

The Kobe airport will be a single-runway domestic airport funded almost entirely by nearly 310 billion yen in bonds issued by the city. Officials hope the airport will be ready for operation by 2005.