(Adds details of tankan, context on Japan's economy)

* March big manufacturers' sentiment index +5 vs Dec -10

* Big non-manufacturers' mood -1 in March vs Dec -5

* Big firms project 3.0% rise in FY2021 capex

By Leika Kihara and Tetsushi Kajimoto

TOKYO, April 1 (Reuters) - Japanese big manufacturers' sentiment improved to pre-pandemic levels in the first quarter as companies planned to increase capital expenditure this year, suggesting the export-reliant economy was benefiting from a solid recovery in global demand.

Confidence among big non-manufacturers also recovered from three months ago, underscoring the fading strains from the coronavirus pandemic, a central bank survey showed on Thursday.

The headline index for big manufacturers' sentiment rose to plus 5 in March from minus 10 in December, the Bank of Japan's closely-watched "tankan" survey showed, marking the third straight quarter of improvement and hitting the highest level since September 2019.

It compared with market forecasts of a flat reading.

The data offers some relief for policymakers striving to revitalise the pandemic-hit economy as a fourth wave of infections raises uncertainty about the outlook.

Big non-manufacturers' sentiment improved to minus 1 in the March survey from minus 5 in December, the survey showed.

Big firms expect to increase capital expenditure by 3.0% in the year that began in April, compared with a median forecast for a 1.4% increase, the survey showed.

Like many countries, Japan deployed massive monetary and fiscal stimulus over the past year to lift the economy back from a record postwar slump.

Many analysts expect the economy to have contracted in the first quarter but see it gradually emerging from the doldrums as solid exports offset some of the weakness in consumption.

The BOJ tankan indexes are derived by subtracting the percentage of pessimistic respondents from optimistic ones. A negative figure means pessimists outnumber optimists. (Reporting by Leika Kihara and Tetsushi Kajimoto; Editing by Sam Holmes)