python - Write stacks of GeoTIFF image to NetCDF by chunk size

I converted GeoTIFF image stacks to NetCDF file with writing data by Index order (layer by layer) (this was a main solution). The problem is, it writes slowly (for 25 images - 1Gb takes 90 seconds). One of the solution is to write the data chunk by chunk not the whole image at once. Does somebody know how to do it or any other solution !?

Code (I used memory to keep images as much as possible then write them all at once)

def tiff_to_netcdf(imagesPath, output, chunksize=None):


    images = []
    for paths, subdirs, files in os.walk(imagesPath):
        for name in files:
            images.append(os.path.join(paths, name))

    ds = gdal.Open(images[0])

    a = ds.ReadAsArray()
    nlat, nlon = np.shape(a)


    b = ds.GetGeoTransform()  # bbox, interval
    lon = np.arange(nlon)*b[1]+b[0]
    lat = np.arange(nlat)*b[5]+b[3]

    basedate = dt.datetime(2006, 01, 11, 0, 0, 0)

    # Create NetCDF file
    # Clobber- Overwrite any existing file with the same name
    nco = netCDF4.Dataset(output+'.nc', 'w', clobber=True)


    # Create dimensions, variables and attributes:
    nco.createDimension('lon', nlon)
    nco.createDimension('lat', nlat)
    nco.createDimension('time', None)

    timeo = nco.createVariable('time', 'f4', ('time',))
    timeo.units = 'days since 2006-01-11 00:00:00'
    timeo.standard_name = 'time'

    lono = nco.createVariable('lon', 'f4', ('lon',))

    lono.standard_name = 'longitude'

    lato = nco.createVariable('lat', 'f4', ('lat',))
    lato.standard_name = 'latitude'

    # Create container variable for CRS: lon/lat WGS84 datum
    crso = nco.createVariable('crs', 'i4')
    crso.long_name = 'Lon/Lat Coords in WGS84'
    crso.grid_mapping_name = 'latitude_longitude'
    crso.longitude_of_prime_meridian = 0.0

    crso.semi_major_axis = 6378137.0
    crso.inverse_flattening = 298.257223563

    # Create short integer variable with chunking
    tmno = nco.createVariable('tmn', 'i2',  ('time', 'lat', 'lon'),
                              zlib=True, chunksizes=chunksize, fill_value=-9999)
    tmno.scale_factor = 0.01
    tmno.add_offset = 0.00
    tmno.grid_mapping = 'crs'
    tmno.set_auto_maskandscale(False)


    nco.Conventions = 'CF-1.6'

    # Write lon,lat
    lono[:] = lon
    lato[:] = lat

    pat = re.compile(r'^(\w{1})(\d{4})(\d{2})(\d{2})_\d{6}___SIG0.*.tif$')
    itime = 0
    written = 0

    data = np.empty((3, 8000, 8000), dtype=np.float)

    # Step through data, writing time and data to NetCDF
    for root, dirs, files in os.walk(imagesPath):
        dirs.sort()
        files.sort()
        for f in files:

            match = re.match(pat, f)
            if match:


                if itime  % 3 == 0 and itime != 0:
                    tmno[written:itime, :, :] = data
                    written = itime
                # read the time values by parsing the filename
                year = int(match.group(2))
                mon = int(match.group(3))
                day = int(match.group(4))
                date = dt.datetime(year, mon, day, 0, 0, 0)
                print(date)

                dtime = (date-basedate).total_seconds()/86400.
                timeo[itime] = dtime
                tmn_path = os.path.join(root, f)
                print(tmn_path)
                tmn = gdal.Open(tmn_path)
                a = tmn.ReadAsArray()  # data
                data[itime%3, :, :] = a
                itime = itime+1



    nco.close()