China's improved foreign trade data for December 2012 has aroused skepticism among some foreign financial institutions recently, but economists told the Global Times Monday that volatility in trade data is not unusual.

According to statistics released by the General Administration of Customs Thursday, the country's exports in December rose 14.1 percent year-on-year to $199.23 billion, while imports increased 6 percent year-on-year.

For the whole year, however, China's exports jumped by the more modest figure of 7.9 percent from the year before, while imports rose 4.3 percent.

The unexpected surge in December's exports has triggered questions from some foreign banks about the reliability of the official data.

"China's December export data came in much stronger than the market expected, which was inconsistent with the PMI new export orders sub-index and the port throughput data," Liu Ligang, chief economist for China at the Australia and New Zealand Banking Group (ANZ), wrote in a research note e-mailed to the Global Times.

"The huge volatility also casts doubts on China's trade data reliability. We found significant inconsistency between China's headline trade figures and the port throughput numbers, highlighting the data accuracy issues," said Liu.

Other foreign banks and financial information providers including Goldman Sachs, UBS and IHS have also raised questions about the unexpected export data, Bloomberg reported Monday.

The customs authorities failed to respond to questions sent by the Global Times by press time Monday, but said they would offer a detailed explanation Tuesday.

"Volatility in foreign trade data is common, because sometimes a large amount of shipments of valuable goods or a change of working days in a single month can make a big difference to the total data," Lu Ting, a Hong Kong-based economist with Bank of America Merrill Lynch, told the Global Times Monday.

Lu said it is well known that monthly year-on-year changes of trade data are volatile. For instance, strikes in California ports in November 2012 could have depressed China's exports to the US in November and then lifted them in December, Lu noted.

China's export growth in November last year was 2.9 percent year-on-year.