SHENZHEN, China, Nov 4 (Reuters) - Chinese property developer Kaisa Group Holdings Ltd missed a payment on a wealth management product (WMP) issued by a unit, a company source said on Thursday, adding to worries about a cash crunch at the debt-strapped firm.

Kaisa Finance in Shenzhen met with more than 100 investors earlier in the day to explain the situation, the person, who declined to be identified due to the sensitivity of the matter, told Reuters.

Kaisa, in common with other heavily-indebted Chinese property developers and conglomerates, issues high-yielding WMPs to mostly mom-and-pop investors - a popular way of borrowing that sidesteps stringent government lending restrictions.

The Shenzhen-based developer has the most offshore debt coming due over the next year of any Chinese developer after embattled China Evergrande Group, which is teetering on the brink of collapse.

Kaisa did not respond to Reuters request for comment.

Hong Kong-listed shares of Kaisa, which has a market value of about $1 billion, plunged more than 14% at one point on Thursday to an all-time low.

Kaisa, which was downgraded by rating agencies last week, has around $3.2 billion in offshore senior notes due in the next 12 months, with the next maturity worth $400 million falling on Dec. 7.

It has coupon payments totalling over $59 million due on Nov. 11 and Nov. 12.

Kaisa's woes come amid concerns about a deepening liquidity crisis in the Chinese property sector, with a string of offshore debt defaults, credit rating downgrading and sell offs in the developers' shares and bonds in recent weeks.

The worsening health of China's $5 trillion property sector, a key economic growth driver, is testing Beijing's resolve to press on with painful structural reforms such as reducing high debt levels.

Analysts at Nomura said this week that conditions in the property sector and the broader economy are likely to deteriorate further in coming months.

Kaisa Finance's headquarters was nearly empty on Thursday morning, with several police vehicles stationed outside the building.

The developer said late on Wednesday its October contracted sales have dropped 30.5% to 8.195 billion yuan , while sales in the first 10 months rose 23%.

Reuters reported last week that Kaisa is seeking buyers for its Hong Kong-listed property management unit, Kaisa Prosperity Holdings Ltd and two residential sites in the city.

Kaisa's bigger rival Evergrande, once China's top-selling developer, is reeling under more than $300 billion in liabilities, fuelling worries about the impact of its fate on the world's second-largest economy as well as on global markets.

Evergrande narrowly averted a default for the second time last week, yet it faces another hard deadline on Nov. 10 for more than $148 million in coupon payments that had been due on Oct. 11. (Reporting by David Kirton in Shenzhen, Clare Jim in Hong Kong and Andrew Galbraith in Shanghai; Editing by Sumeet Chatterjee and Kim Coghill)