Japan's payments-clearing network suffered a system problem Tuesday, affecting 11 banks including MUFG Bank and disrupting at least 1.4 million transactions, the network's operator said.

Japanese Banks' Payment Clearing Network said it was unclear what went wrong and when the problem would be fixed. It is the first time that bank customers have been impacted by a system problem since the network was launched in 1973.

The system problem had not been solved as of Tuesday night, but the network operator expects to process 1 million of the disrupted transactions by the end of Tuesday using backup measures, it said.

Resona Bank and JPMorgan Chase Bank were among those hit, the operator said.

Both Mizuho Bank and Sumitomo Mitsui Banking Corp. said they were experiencing delays in transferring money to and from some banks.

MUFG Bank said money transfers to other banks via ATMs, including those at some convenience stores, and online banking could not be processed. The Japanese megabank added it was also unable to receive funds transferred from those banks.

Resona Bank said funds could not be transferred to other banks, warning it was possible such transactions not be completed Tuesday.

Most Japanese banks are connected to the key payment network, known as the Zengin system, which processes an average 6.5 million transactions and over 12 trillion yen ($81 billion) a day.