WASHINGTON -- Spending on U.S. construction projects surged in September to their second-highest level on record as spending on nonresidential buildings such as offices and factories hit all-time highs.

The Commerce Department said U.S. construction spending rose 2.4% to an annual rate of $819.3 billion after a 1.8% gain in August.

September's gains were much stronger than the 0.4% gain forecast by economists in a Reuters poll and was the largest percentage gain since a 2.6% rise in November of 1999. That took construction spending to its second-highest rate ever. Construction spending hit its peak in March of this year when it stood at $829.5 billion. It steadily declined every month until July before posting gains in August and September.

Spending on private construction rose 2.1% to an annual rate of $630.8 billion, the second-highest rate ever after March's peak. Spending on nonresidential buildings hit an all-time high, rising a strong 3.4% to an annual rate of $229.1 billion.

Within the private construction sector a slew of all-time highs were reached, including industrial projects, offices and educational projects as well as on hospitals and institutions.

Spending on public construction projects also posted strong gains, rising 3.5% to an annual rate of $188.5 billion. Within that category, spending on educational projects and miscellaneous public construction projects posted records.

While most recent economic indicators have painted a picture of a slowing U.S. economy, this latest report is among those that will keep the inflation-wary Federal Reserve on alert for possible signs that the pace of economic growth may begin to re-ignite as the year draws to a close.