OSAKA -- Phone services that had been disrupted for two hours in most of Osaka Prefecture were restored to normal a little past noon on Monday, said NTT West Corp., a regional unit of Nippon Telegraph and Telephone Corp.

The carrier said it couldn't immediately determine the cause of the two-hour disruption, which affected most of the 5.16 million lines it provides.

NTT West said the disruptions may have occurred because many people phoned to order event tickets or because people made many calls after the end of the weekend.

"I can't think of any other reason than that a massive number of phone lines were used at the same time for some reason," an NTT West official said.

But because no major ticket sales can be confirmed and the disruptions affected a wide area for a long time, the company said it is also looking into other possibilities.

The phone carrier was inundated with calls that were more than 10 times the normal volume.

At 10:45 a.m., it limited the amount of calls that could be placed.

The company had never experienced such a problem since it was formed through a breakup of the former government monopoly in 1999.

Call disruptions, which affected 5 million lines, were experienced with telephone numbers starting with the 06 and 072 prefixes, which are used in most of the prefecture and the city of Amagasaki, Hyogo Prefecture.

Service disruptions began at around 10 a.m. on fixed-line calls made and received in the prefecture. Calls to cell phones and those made from Tokyo also encountered problems.

Company employees scrambled to control the situation as they began having trouble contacting other employees or their customers via fixed-line phones.

One employee of Kurokawa Kitoku Securities Co., a brokerage in Chuo Ward, Osaka, complained of not being able to take calls from her clients.

"We can't do business unless we can receive calls ordering transactions," she said.

An official of a midsize brokerage in Osaka said the disruptions did not affect its operations because most of the firm's clients use cell phones to contact it.

The official, however, expressed worry that long disruptions could have an impact on its volume of transactions.

At Sanyo Electric Co., a major consumer electronics firm, employees communicated with one another via cell phones.

"We haven't felt an impact on our operations so far," a Sanyo official said before the services were restored.

An official of a bank operating in the city said that telephone banking services were disrupted, but no disruptions were confirmed at automated teller machines.

Osaka Prefectural Police said they have not had problems with their phones.

A public relations official at Takashimaya Co., a major department store in Chuo Ward, said the store was getting half the number of calls it normally gets during this gift-giving season.