The officials said conventional and cellular telephones became nearly unworkable as their lines grew busy.
The trouble has affected domestic and international phone calls. Workers of the semi-governmental Japan External Trade Organization in Auckland said they suspect trouble has occurred on portable phone networks.
No trouble has occurred in the country in connection with the Internet, gas and water supplies, automated teller machines or credit card services.
The Y2K bug could cause computer systems with software that identifies years only by their last two digits to crash or malfunction on Jan. 1, 2000. In Japan, mobile phones are operating normally although there are some connection problems related to the usual year-end flood of calls, a spokesman for Japan's largest mobile phone company said today.
"There are some communication problems in relation to the year-end festivities, but nothing major," said a spokesman for NTT Mobile Communications Network (NTT Docomo).
Earlier in the day, two types of digital cell phones sold by IDO and eight companies under DDI's cellular telephone group failed to display the proper date, but company officials said it was not related to Y2K computer bug problems.
The cell phones, made by Kyocera, displayed Dec. 31, 2000, instead of Dec. 31, 1999, when turned off and running on backup power, company officials said.
Reuters contributed to this report.